Provided by: ddpt_0.97-1_amd64 
NAME
ddpt - copies data between files and storage devices. Support for devices that understand the SCSI
command set.
SYNOPSIS
ddpt [bpt=BPT[,OBPC]] [bs=BS] [cdbsz=IO_CDBSZ] [cdl=CDL] [coe={0|1}] [coe_limit=CL] [conv=CONVS]
[count=COUNT] [ddpt=VERS] [delay=MS[,W_MS]] [ibs=IBS] [id_usage=LIU] if=IFILE [iflag=FLAGS] [intio={0|1}]
[iseek=SKIP] [ito=ITO] [list_id=LID] [obs=OBS] [of=OFILE] [of2=OFILE2] [oflag=FLAGS] [oseek=SEEK]
[prio=PRIO] [protect=RDP[,WRP]] [retries=RETR] [rtf=RTF] [rtype=RTYPE] [seek=SEEK] [skip=SKIP]
[status=STAT] [to=TO] [verbose=VERB] [--dry-run] [--flexible] [--help] [--job=JF] [--odx] [--prefetch]
[--progress] [--quiet] [--verbose] [--verify] [--version] [--wscan] [--xcopy] [ddpt] [JF]
For comparison here is the synopsis for GNU's dd command:
dd [bs=BS] [cbs=CBS] [conv=CONVS] [count=COUNT] [ibs=IBS] [if=IFILE] [iflag=FLAGS] [obs=OBS] [of=OFILE]
[oflag=FLAGS] [seek=SEEK] [skip=SKIP] [status=STAT] [--help] [--version]
DESCRIPTION
Copies data between files or simply reads data from a file. Alternatively if the --verify option is
given, the IFILE and OFILE contents are compared, stopping if an inequality is found. This utility is
specialized for "files" that are storage devices, especially those that can use the SCSI command sets
(e.g. SATA and SAS disks). It can issue SCSI commands in pass-through ("pt") mode. Similar syntax and
semantics to the Unix dd(1) command.
For comparison, the SYNOPSIS section above shows both the ddpt command line operands and options followed
by GNU's dd(1) command line operands and options. Broadly speaking ddpt can be considered a super-set of
dd. See the section on DD DIFFERENCES for significant differences between ddpt and dd.
This utility either does direct copies, based on read-write sequences, or offloaded copies. In an
offloaded copy the data being copied does not necessarily pass through the memory of the the machine
originating the copy operation; this can save a significant amount of time and lessen CPU usage.
When doing a direct copy, this utility breaks the copy into segments since computer RAM is typically a
scarce resource. First it reads in BPT*IBS bytes from IFILE (or less if near the end of the copy) into a
copy buffer. In the absence of the various operand and flags that bypass the write operation, the copy
buffer is then written out to OFILE. The copy process continues working its way along IFILE and OFILE
until either COUNT is exhausted, an end of file is detected, or an error occurs. If IBS and OBS are
different, ddpt restricts the value of OBS such that the copy buffer is an integral number of output
blocks (i.e. (((IBS * BPT) % OBS) == 0) ). In the following descriptions, "segment" refers to all or part
of a copy buffer.
The term "pt device" is used for a pass-through device to which SCSI commands like READ(10), WRITE(10) or
POPULATE TOKEN may be sent. A pt device may only be able to process SCSI commands in which case the "pt"
flag is assumed. The ability to recognize such a pt only device may vary depending on the operating
system (e.g. in Linux /dev/sg2 and /dev/bsg/3:0:1:0 are recognized). However if a device can process
either normal UNIX read()/ write() calls or pass-through SCSI commands then the default is to use UNIX
read()/write() calls. That default can be overridden by using the "pt" flag (e.g. "if=/dev/sdc
iflag=pt"). When pt access is specified any partition information is ignored. So "if=/dev/sdc2 iflag=pt
skip=3" will start at logical block address 3 of '/dev/sdc'. As a protection measure ddpt will only
accept that if the force flag is also given (i.e. 'iflag=pt,force').
This utility supports two types of offloaded copies. Both are based on the EXTENDED COPY (XCOPY or xcopy)
family of SCSI commands. The first uses the XCOPY(LID1) command to do a disk to disk copy. LID1 stands
for List IDentifier length of 1 byte and the commands are described in the SPC-4 and earlier SPC-3 and
SPC-2 standards. The SPC-4 standard (ANSI INCITS 513-2015) added the XCOPY(LID4) sub-family of copy
offloaded commands. Now SPC-5 drafts have dropped the LID1 variants and removed the LID4 suffix on the
remaining XCOPY family of commands. To differentiate, this man page will continue to use the LID1 and
LID4 suffixes. There is a subset of XCOPY(LID4), specialized for offloaded disk to disk copies, that is
known by the market name: ODX. In the descriptions below "xcopy" refers to copies based on XCOPY(LID1)
while "odx" refers to either full or partial ODX copies. See the XCOPY and ODX sections below for more
information.
The syntax of the dd command is somewhat unique in Unix and ddpt follows in a similar fashion. Operands
(i.e. those with the <name>=<something> structure) are shown in OPERANDS section. The more familiar Unix
options (i.e. those starting with one or two hyphens) are shown in the OPTIONS section. Then there are a
few arguments which are command line entities that are neither operands nor options, see the ARGUMENTS
section.
OPERANDS
The operands are listed alphabetically (by <name>) below. The <name> is the part that is to the left of
the equal sign. All <names> start with a lower case alphabetical character.
bpt=BPT[,OBPC]
where BPT is Blocks Per Transfer. A direct copy is made up of multiple transfers, each first
reading BPT input blocks (i.e. BPT * IBS bytes) from IFILE into the copy buffer and then from that
copy buffer writing (BPT * IBS) / OBS output blocks to OFILE. This continues until the copy is
finished, with the last transfer being potentially shorter. The default BPT value varies depending
on IBS. When IBS < 8, BPT is 8192; when IBS < 64, BPT is 1024; when IBS < 1024, BPT is 128; when
IBS < 8192, BPT is 16; when IBS < 32768, BPT is 4; else BPT defaults to 1. If BPT is given as 0 it
is treated as the default value. For "bs=512", BPT defaults to 128 so that 64 KiB (or less) is
read from IFILE into the copy buffer. This operand is treated differently in ODX and is typically
only needed for testing; see ODX section.
The optional OBPC (Output Blocks Per Check) argument controls the granularity of sparse writes,
write sparing and trim checks. The default granularity is the size of the copy buffer (i.e. BPT *
IBS bytes). That can be reduced by specifying OBPC. The finest granularity is when OBPC is 1 which
implies the unit of each check is OBS bytes. When OBPC is 0, or not given, the default
granularity is used. Large OBPC values are rounded down so that OBPC*OBS does not exceed the size
of the copy buffer.
odx: may be used to limit the data represented by each ROD. Mainly for testing.
If BPT is too large on Linux, the obscure "Invalid argument" error value (EINVAL) is returned.
bs=BS where BS is the IFILE and OFILE block size in bytes. Conflicts with either the "ibs=" or "obs="
operands. The value of BS is placed in IBS and OBS. If IFILE or OFILE is a "pt" device then BS
must be the logical block size of the device. See the DD DIFFERENCES section below. The default is
512 bytes unless overridden by the DDPT_DEF_BS environment variable. Note that newer disks use
4096 byte blocks with perhaps larger block sizes coming in the future. CD/DVD/BD media use a
logical block size of 2048 bytes.
cdbsz=IO_CDBSZ
size of SCSI READ and/or WRITE (VERIFY) command descriptor blocks (cdb) in bytes. IO_CDBSZ may be
one number or two numbers separated by a comma. The acceptable numbers are 0, 6, 10, 12, 16 or
32. The default 0 will usually be set to 10 internally unless the (first and last) LBAs cannot fit
in 32 bits in which case the 16 byte variant of each command is used. If one number is given it
applies both to the IFILE and IFILE. If two numbers are given, the first applies to the IFILE
(i.e. the READ command) and the second applies to the OFILE.
If IFILE or OFILE is not a SCSI pass-through device then the corresponding IO_CDBSZ value is
ignored.
cdl=CDL
allows setting of command duration limits. CDL is either a single value or two values separated by
a comma. If one value is given, it applies to both IFILE and OFILE (if they are pass-through
devices). If two values are given, the first applies to IFILE while the second applies to OFILE.
The value may be from 0 to 7 where 0 is the default and means there are no command duration
limits. Command duration limits are only supported by 16 and 32 byte READ and WRITE commands (and
the WRITE SCATTERED command which is not used by this utility). If the cdbsz operand is not given
and would have a value less than 16, then if CDL is greater than 0, the cdbsz is increased to 16.
Command duration limits can be accesses and changed in the Command duration limit A and B mode
pages, plus the Command duration limit T2A and T2B mode pages. The sdparm utility may be used to
access and change these mode pages.
coe={0|1}
set to 1 for continue on error. Applies to errors on input and output for pt devices but only on
input from block devices or regular files. Errors on other files will stop ddpt. Default is 0
which implies stop on any error. See the 'coe' flag for more information.
coe_limit=CL
where CL is the maximum number of consecutive bad blocks stepped over due to "coe=1" on reads
before the copy terminates. The default is 0 which is implies no limit. This operand is meant to
stop the copy soon after unrecorded media is detected while still offering "continue on error"
capability for infrequent, randomly distributed errors.
conv=CONVS
see the CONVERSIONS section below.
count=COUNT
copy COUNT input blocks from IFILE to OFILE. If this operand is not given (or COUNT is '-1') then
the COUNT may be deduced from either IFILE or OFILE. See the COUNT section below.
If a 'hard' gather list is given to skip=SKIP or a 'hard' scatter list is given to seek=SEEK then
typically count=COUNT should not be supplied. This is because a 'hard' scatter gather list implies
a transfer count. If both are given then ddpt will exit if they are unequal, the force flag can be
used to override this action. See the SCATTER GATHER LISTS section below for a discussion of
'hard' and 'soft' scatter gather lists.
ddpt=VERS
causes a syntax error while parsing the command line if the current version of the ddpt utility is
less than VERS. VERS can take one of two forms: starting with a digit in which case is should have
the form "<major_vn>.<minor_vn>" or starting with the letter "r" followed by "<svn.rev>". The
latter case is the subversion revision number. Both numbers can be found in the output of the
--version option. The purpose of this operand is to be placed in job files so that they are not
run on older versions of this utility
delay=MS[,W_MS]
after each segment is copied (typically every (IBS * BPT) bytes) a delay (sleep) of MS
milliseconds is performed. The default value for MS is 0 which implies no delay. If W_MS is given
and greater than 0 (its default value) then there is an additional delay of W_MS milliseconds
associated with each actual write operation that is performed. If MS is greater than 0 then there
is not a delay before the first copy segment (or after the last); if W_MS is greater than 0 then
there is not a delay before the first write segment. These delays can be used for a bandwidth
limiting.
odx: the MS delay is implemented in the same fashion after each ROD is copied, apart from the
last. If W_MS is greater than 0 then that delay occurs before each WUT command, apart from the
first.
ibs=IBS
where IBS is the IFILE block size in bytes. The default value is BS or its default (512).
Conflicts the "bs=" operand (i.e. giving both "bs=512 ibs=512" is considered a syntax error).
id_usage=LIU
xcopy: SCSI EXTENDED COPY parameter list LIST ID USAGE field is set to LIU. The default value is 0
or 2 . LIU can be a number between 0 and 3 inclusive or a string. The strings can be either:
'hold' for 0, 'discard' for 2 or 'disable' for 3.
if=IFILE
read from IFILE. If IFILE is '-' then stdin is read. Starts reading at the beginning of IFILE
unless SKIP is given.
This operand must be given (apart from one odx case and when iflag=00 or iflag=ff is given).
odx: the rtf=RTF operand may replace the if=IFILE operand as input. See the ODX section.
iflag=FLAGS
where FLAGS is a comma separated list of one or more flags outlined in the FLAGS section below.
These flags are associated with IFILE and are mostly ignored when IFILE is stdin.
intio={0|1}
set to 1 for allow signals (SIGINT, SIGPIPE and SIGUSR1 (or SIGINFO)) to be received during IO
from IFILE or IO to OFILE or OFILE2. Default is 0 which causes these signals to be masked during
IO operations with a check for signals prior each IO. As long as IO operations don't lock up (e.g.
SCSI READ and WRITE commands) the default is the safer option. Even if IO operations do lock up it
is best to let the kernel take care of that.
iseek=SKIP
in its simplest form, SKIP is a single number: start reading after SKIP blocks (each of IBS bytes)
from the start of IFILE. Default is block 0 (i.e. start of file). This operand is a synonym for
skip=SKIP, see its description.
ito=ITO
odx: ITO is the inactivity timeout whose units are seconds. The default value is 0 which means the
copy manager will take the default inactivity timeout value from the Block Device ROD Token Limits
descriptor in the Third Party Copy VPD page. ITO is ignored if it it exceeds the maximum
inactivity timeout value in the same descriptor (unless the force flag is given).
list_id=LID
LID is the xcopy LIST IDENTIFIER field or the STR_ID field for the WRITE STREAM command. Fo xcopy
it is used to associate an originating xcopy command with follow-up commands such as RECEIVE ROD
TOKEN INFORMATION. If given, the LID should not clash with any other xcopy LID currently in use on
this I_T nexus.
xcopy: LID is a 1 byte (8 bit) value whose default value is 1 or, if id_usage=disable, 0 . LID
must not exceed 255.
odx: LID is a 4 byte (32 bit) value whose default value is 257 (i.e. 0x101) and, if a second
default is needed, 258 (0x102) is used. If a clash is detected on the default list identifier
value then the next higher value is tried (stopping after 10 attempts).
oflag=wstream: LID is a 2 byte (16 bit) value whose default value is 0. It is the Stream
Identifier (STR_ID field) for the WRITE STREAM(16) command. Valid Stream identifiers are 0x1 to
0xffff (65535) inclusive, so the default value of 0 is invalid.
obs=OBS
where OBS is the OFILE block size in bytes. The default value is BS or its default (512).
Conflicts the "bs=" operand (e.g. giving both "bs=512 obs=512" is considered a syntax error). If
OBS is given then it has the following restriction: the integer expression (((IBS * BPT) % OBS) ==
0) must be true. Stated another way: the copy buffer size must be an integral multiple of OBS. If
of2=OFILE2 is given then OBS is its block size as well.
of=OFILE
write to OFILE. The default value is /dev/null . If OFILE is '-' then writes to stdout. If OFILE
is /dev/null then no actual writes are performed. If OFILE is '.' (period) then it is treated the
same way as /dev/null . If OFILE exists then it is _not_ truncated unless "oflag=trunc" is given.
See section on DD DIFFERENCES.
odx: if this operand (of=OFILE) is not given and the rtf=RTF operand is given then the RTF file
may be thought of as receiving the output in the form of one or more ROD Tokens. See the ODX
section.
of2=OFILE2
write output to OFILE2. The default action is not to do this additional write (i.e. when this
operand is not given). OFILE2 is assumed to be a regular file or a fifo (i.e. a named pipe).
OFILE2 is opened for writing and is created if necessary. If OFILE2 is a fifo (named pipe) then
some other command should be consuming that data (e.g. 'md5sum OFILE2'), otherwise this utility
will block. The write to OFILE2 occurs before the write to OFILE and prior to sparse writing and
write sparing logic. So everything read is written to OFILE2.
OFILE2 is not truncated before writing. Assuming that the OFILE2 length is shorter than what is
written (or it is created) then its contents should be the concatenation of all segments (each of
ibs*bpt bytes long, with the last segment being possibly shorter). The gather list given to
skip=SKIP effects what is read into each segment so it indirectly effects what is written to
OFILE2. However the scatter list given to seek=SEEK has no effect on what is written to OFILE2.
oflag=FLAGS
where FLAGS is a comma separated list of one or more flags outlined in the FLAGS section. These
flags are associated with OFILE and are ignored when OFILE is /dev/null, '.' (period), or stdout.
oseek=SEEK
start writing SEEK blocks (each of OBS bytes) from the start of OFILE. Default is block 0 (i.e.
start of file). This operand is a synonym for seek=SEEK, see its description.
prio=PRIO
xcopy: SCSI EXTENDED COPY parameter list PRIORITY field is set to PRIO. The default value is 1 .
protect=RDP[,WRP]
where RDP is the RDPROTECT field in SCSI READ commands and WRP is the WRPROTECT field in SCSI
WRITE commands. The default value for both is 0 which implies no additional protection information
will be transferred. Both RDP and WRP can be from 0 to 7. If RDP is greater than 0 then IFILE
must be a pt device. If WRP is greater than 0 then OFILE must be a pt device.
When copying data plus protection information from one disk to another then 'protect=3,3' will
give the least number of problems as that combination then of PI checking on both the read and
write side. See the PROTECTIO INFORMATION section below.
retries=RETR
sometimes retries at the host are useful, for example when there is a transport error. When RETR
is greater than zero then SCSI READs and WRITEs are retried on error, RETR times. Default value is
zero. Only applies to errors on pt devices.
rtf=RTF
odx: where RTF is a filename. One or more ROD tokens are written to RTF during a read to tokens
variant or a full copy variant. One or more ROD tokens are read from RTF during a write from token
variant. This operand is not required on a full copy variant. ROD Tokens are 512 bytes long and
an extra 8 byte (big-endian) integer containing the 'number of bytes represented' is placed after
each ROD Token if rtf_len is given.
rtype=RTYPE
odx: where RTYPE is the ROD Type. The default value (0) indicates that the copy manager (in the
source) decides. RTYPE can be a decimal number, a hex number (prefixed by 0x or with a "h"
appended) or one of "pit-def", "pit-vuln", "pit-pers", "pit-cow", "pit-any" or "zero". The final
truncated word can be spelt out (e.g. "pit-vulnerable"). The "pit-" prefix is a shortening of
"point in time" copy. The "zero" causes a special Block device zero Token to be created.
seek=SEEK
start writing SEEK blocks (each of OBS bytes) from the start of OFILE. Default is block 0 (i.e.
start of file). The SEEK value may exceed the number of OBS-sized blocks in OFILE.
SEEK can be a scatter (gather) list: see the SCATTER GATHER LISTS section below.
skip=SKIP
start reading SKIP blocks (each of IBS bytes) from the start of IFILE. Default is block 0 (i.e.
start of file). The SKIP value must be less than the number of IBS-sized blocks in IFILE.
SKIP can be a (scatter) gather list: see the SCATTER GATHER LISTS section below.
status=STAT
the STAT value of 'noxfer' suppresses the throughput speed and the copy time reporting at the end
of the copy. A STAT value of 'none' additionally suppresses the records in and out reporting after
the copy. So 'status=none' makes ddpt act like a traditional Unix command in which "no news is
good news". The default action of ddpt is to show the throughput (in megabytes per second) and
the time taken to do the copy after the "records in" and "records out" lines at the end of the
copy. A STAT value of 'sgl' together with '-vv' option will print internally generated scatter
gather lists before the copy begins. When the '-vv' options is given alone then internal scatter
lists headers are printed, but not individual elements. In most cases these scatter gather lists
will be the same lists given to the seek=SEEK and skip=SKIP operands. As a convenience the value
'null' is accepted for STAT and does nothing.
A STAT value of 'progress' prints a progress report (to stderr) every two minutes. If 'progress'
is used twice, either by repeating the 'status=progress' operand or by entering
'status=progress,progress', then a progress report is printed every minute. If it is used thrice,
the a progress report is printed every 30 seconds. Note that care is taken not to flood the OS
with calls to check the time which would slow down the copy process. The amount of data output by
the progress reports can modified at runtime (e.g. during a long copy). If the verbose flag is 0
or 1 (but not higher and not if the --quiet option is given) then sending a SIG_USR1 (or SIGINFO
in FreeBSD) signal to the running ddpt process will toggle the verbose flag between 0 and 1. Note
there is now a shorter form, the command line option: --progress or simply '-p'.
Note that GNU's dd supports 'noxfer', 'none' and 'progress' with similar semantics.
to=TO odx, xcopy: where TO is am xcopy originating command timeout in seconds. The default value is 0
which is converted internally to 600 seconds (10 minutes). Best to set this timeout value well
above the expected copy time. In a odx full copy this timeout is applied to both the POPULATE
TOKEN and WRITE USING TOKEN commands.
verbose=VERB
as VERB increases so does the amount of debug reporting sent to stderr. Default value is zero
which yields the minimum amount of debug reporting. A value of 1 reports extra information that
is not repetitive. A value 2 reports cdbs and responses for SCSI commands that are not repetitive
(i.e. other that READ and WRITE). Error processing is not considered repetitive. Values of 3 and 4
yield reporting for all SCSI commands, plus Unix read() and write() calls, so there can be a lot
of output.
If VERB is "-1" then reporting that would have been sent to stderr is redirected to /dev/null
essentially throwing it away. It has the same action as the --quiet option.
In some cases the position of verbose=VERB (or --verbose) on the command line is significant. For
example to debug (or at least list out) a scatter gather list given to skip=SKIP or seek=SEEK the
verbose=VERB operand (or --verbose) should appear before skip and/or seek.
OPTIONS
Options are listed in alphabetical order, sorted by their long name.
-d, --dry-run
does all the operand and option processing, opens given file and devices but bypasses the copy
stage. For complex command line invocations or for testing invocations to be placed in script
files, this option may be useful to check for syntax and related errors.
When used once the logic bypasses the copy just before it would normally start copying. When used
twice (or more) it goes deeper into the copy to the IO call level before bypassing the calls. To
see (on stderr) information for each IO this option combination may be useful: '-ddvv'.
-f, --flexible
this option currently only effects the parsing of sgl_s in files that are in hexadecimal plus they
have a leading line with 'HEX' in them. Without this option any such line must be invoked with
'H@' before the filename; in other words the 'H' in the invocation needs to match the HEX in the
file. With this option a sgl in a file can be invoked with '@' and if a line with HEX is parsed
before any LBA,NUM pairs then it switches to hexadecimal mode; so all the parsed LBA,NUM pairs are
assumed to be in hexadecimal.
-h, --help
reports usage message then exits.
--job=JF
where JF is a file name. That file can contain operands and options listed in this and the
previous sections. See the JOB FILES section below.
-o, --odx
indicates to this utility that one of the four odx variants is requested. See ODX section.
-P, --prefetch
this option is only active when the --verify option is also given. It causes the SCSI
PRE-FETCH(OFILE, IMMED) command to be sent at the start of each copy segment. See the VERIFY
section below.
-p, --progress
this option has the same effect as status=progress but is shorter to type and easier to remember.
When given once, the default reporting period is two minutes, if given twice (e.g. '-pp') that
period is shortened to one minute.
-q, --quiet
redirects the messages (sent to stderr) to /dev/null which is essentially throwing them away. That
redirect takes place after the command line operands and options are parsed and associated sanity
checks performed.
-v, --verbose
equivalent of verbose=1. If --verbose appears twice then that is equivalent to verbose=2. Also -vv
is equivalent to verbose=2.
-X, --verify
rather than copy, a comparison is done between IFILE and OFILE. The compare continues until an
inequality is found at which point the operation stops. This is only available if OFILE is a
pass-through device that implements VERIFY(10 or 16) with BYTCHK set to 1. See the VERIFY section
below.
-V, --version
reports version number information then exits.
-w, --wscan
this option is available in Windows only. It lists storage device names and the corresponding
volumes, if any. When used twice it adds the "bus type" of the closest transport (e.g. a SATA disk
in a USB connected enclosure has bus type USB). When used three times a SCSI adapter scan is
added. When used four times only a SCSI adapter scan is shown. See EXAMPLES section below and the
README.win32 file.
-x, --xcopy
this option will attempt to call the SCSI EXTENDED COPY(LID1) command. In the absence of another
indication the xcopy command will be sent to the destination (i.e. OFILE). See the section on
ENVIRONMENT VARIABLES below.
ARGUMENTS
Arguments do not start with hyphen nor contain a "=".
ddpt this string is just a marker. It must not appear in the command line and it must appear in the
contents of a job file that isn't part of a comment (i.e. following a "#" on a line). A syntax
error is generated (and no copy occurs) if these rules are violated.
JF a command line element that does not contain a '=' (i.e. a ddpt operand) and does not start with
'-', apart from the string "ddpt" is treated as a job file (i.e. JF). See the JOB FILES section
below.
CONVERSIONS
One or more conversions can be given to the "conv=" option. If more than one is given, they should be
comma separated. ddpt does not perform the traditional dd conversions (e.g. ASCII to EBCDIC). Recently
added conversions inherited from GNU's dd overlap somewhat with the some of ddpt flags.
fdatasync
equivalent to "oflag=fdatasync". Flushes data associated with the OFILE to storage at the end of
the copy. This conversion is for compatibility with GNU's dd.
fsync equivalent to "oflag=fsync". Flushes data and meta-data associated with the OFILE to storage at
the end of the copy. This conversion
no_del_tkn
equivalent to "oflag=no_del_tkn".
nocreat
OFILE will not be created if it doesn't exist. The default action if OFILE does not exist is to
create a regular file (then write into it). The default action can be surprising if writing to a
device node in /dev and due to some external action (e.g. a USB key being removed) that device
node name disappears.
noerror
this conversion is very close to "iflag=coe" and is treated as such. See the "coe" flag. Note that
an error on a block device or regular file OFILE will stop the copy.
notrunc
this conversion is accepted for compatibility with dd and ignored since the default action of this
utility is not to truncate OFILE.
null has no affect, just a placeholder.
prefer_rcs
equivalent to "oflag=prefer_rcs".
resume See "resume" in the FLAGS sections for more information.
rtf_len
equivalent to "oflag=rtf_len".
sparing
See "sparing" in the FLAGS sections for more information.
sparse FreeBSD's dd supports "conv=sparse" and now GNU's dd does as well so the same syntax is supported
in ddpt. See "sparse" in the FLAGS sections for more information.
sync is ignored by ddpt. With dd it means supply zero fill (rather than skip) and is typically used
like this "conv=noerror,sync" to have the same functionality as ddpt's "iflag=coe".
trunc if OFILE is a regular file then truncate it prior to starting the copy. See "trunc" in the FLAGS
section.
FLAGS
A list of flags and their meanings follow. The flag name is followed by one or two indications in square
brackets. The first indication is either "[i]", "[o]" or "[io]" indicating this flag is active for the
IFILE, OFILE or both the IFILE and the OFILE. The second indication contains some combination of "reg",
"blk" "pt", "odx", or "xcopy". These indicate whether the flag applies to a regular file, a block device
(accessed via Unix read() and write() commands, a pass-through device, an ODX offloaded copy or a
XCOPY(LID1) offloaded copy respectively. Other special file types that are sometimes referred to are
"fifo" and "tape".
00 [i] This flag may replace IFILE with a source of zero (0x0) bytes. If IFILE is given and is shorter
than OFILE then it continues to copy after IFILE is exhausted supplying zero fill bytes. Can only
be used on input. Zeros can also be generated by using "if=/dev/zero" or an equivalent.
If both '00' and 'ff' flags are given then a marching byte pattern is placed in the segment prior
to writing it out. It starts at 0x0 and wraps after 0xff (if the segment is large enough, as it
usually is).
append [o] [reg], [io] [odx]
causes the O_APPEND flag to be added to the open of OFILE. For regular files this will lead to
data being appended to the end of any existing data. Conflicts the seek=SEEK option. The default
action of this utility is to overwrite any existing data from the beginning of OFILE or, if SEEK
is given, starting at block SEEK. Note that attempting to 'append' to a device file (e.g. a disk)
will usually be ignored or may cause an error to be reported.
odx: if the rtf=RTF option is given, RTF exists, is a regular file and this utility wants to write
to RTF then new ROD Tokens are appended to RTF. The default action is to truncate RTF before new
ROD Tokens are written to it.
atomic [o] [pt]
this flag changes the pass-through SCSI WRITE command to the SCSI WRITE ATOMIC(16) command on
OFILE (and the cdbsz={6|10|12|16|32} option is ignored for OFILE). If this flag is applied to
IFILE or to a non pass-through file then it is ignored.
block [io] [pt]
pass-through file opens are non-blocking by default and may report the pt device is busy. Use this
flag to open blocking so utility may wait until another process locking (or with an exclusive
open) is complete before continuing.
bytchk [o] [pt]
only active when used together with oflag=wverify. Sets the BYTCHK field in the SCSI WRITE AND
VERIFY command. Since that field is two bits wide, this flag can be specified multiple times (up
to three) to place the corresponding value in the field.
cat [io] [xcopy]
xcopy: set CAT (residual data handling) bit in EXTENDED COPY(LID1) parameter list segment
descriptor header. May appear in either flag list when xcopy is being used. Works with the PAD bit
for handling residual data on the destination side. See the XCOPY section below.
coe [io] [pt], [i] [reg,blk]
continue on error. 'iflag=coe oflag=coe' and 'coe=1' are equivalent. Errors occurring on output
regular or block files will stop ddpt. Error messages are sent to stderr. This flag is similar to
'conv=noerror,sync' in the dd(1) utility. Unrecovered errors are counted and reported in the
summary at the end of the copy.
This paragraph concerns coe on pt devices. A medium, hardware or blank check error during a read
operation will will cause the following: first re-read blocks prior to the bad block, then try to
recover the bad block (supplying zeros if that fails), and finally re-read the blocks after the
bad block. A medium, hardware or blank check error while writing is reported but otherwise
ignored. SCSI disks may automatically try and remap faulty sectors (see the AWRE and ARRE in the
read write error recovery mode page (the sdparm utility can access these attributes)). If bad LBAs
are reported by the pass-through then the LBA of the lowest and highest bad block is also
reported.
This paragraph concerns coe on input regular files and block devices. When a EIO or EREMOTEIO
error is detected on a normal segment read then the segment is re-read one block (i.e. IBS bytes)
at a time. Any block that yields a EIO or EREMOTEIO error is replaced by zeros. Any other error, a
short read or an end of file will terminate the copy, usually after the data that has been read is
written to the output file.
dc [io] [blk,pt]
xcopy: set DC (destination counter) bit in EXTENDED COPY(LID1) parameter list segment descriptor
header. May appear in either flag list when xcopy is being used.
direct [io] [reg,blk]
causes the O_DIRECT flag to be added to the open of IFILE and/or OFILE. This flag requires some
memory alignment on IO. Hence user memory buffers are aligned to the page size. May have no effect
on pt devices or cause an error (e.g. Linux seems to dis-allow O_DIRECT on character devices (like
sg devices) yielding EINVAL). This flag will bypass caching/buffering normally done by block
layer. Beware of data coherency issues if the same locations have been recently accessed via the
block layer in its normal mode (i.e. non-direct). See open(2) man page.
dpo [io] [pt]
set the DPO bit (disable page out) in SCSI READ and WRITE commands. Not supported for 6 byte cdb
variants of READ and WRITE. Indicates that data is unlikely to be required to stay in device (e.g.
disk) cache. May speed media copy and/or cause a media copy to have less impact on other device
users.
errblk [i] [pt] [experimental]
attempts to create or append to a file called "errblk.txt" in the current directory the logical
block addresses of blocks that cannot be read. The first (appended) line is "# start <timestamp>".
That is followed by the LBAs in hex (and prefixed with "0x") of any block that cannot be read, one
LBA per line. If the sense data does not correctly identify the LBA of the first error in the
range it was asked to read then a LBA range is reported in the form of the lowest and the highest
LBA in the range separated by a "-". At the end of the copy a line with "# stop <timestamp>" is
appended to "errblk.txt". Typically used with "coe".
excl [io] [reg,blk]
causes the O_EXCL flag to be added to the open of IFILE and/or OFILE. See open(2) man page.
fdatasync [o] [reg,blk]
Flushes data associated with the OFILE to storage at the end of the copy.
ff [i] This flag may replace IFILE with a source of 0xff bytes. If IFILE is given and is shorter than
OFILE then it continues to copy after IFILE is exhausted supplying 0xff fill bytes. Can only be
used on input.
If both '00' and 'ff' flags are given then a marching byte pattern is placed in the segment prior
to writing it out. It starts at 0x0 and wraps after 0xff (if the segment is large enough, as it
usually is).
flock [io] [reg,blk,pt]
after opening the associated file (i.e. IFILE and/or OFILE) an attempt is made to get an advisory
exclusive lock with the flock() system call. The flock arguments are "FLOCK_EX | FLOCK_NB" which
will cause the lock to be taken if available else a "temporarily unavailable" error is generated.
An exit status of 90 is produced in the latter case and no copy is done. See flock(2) man page.
force [io] [pt] [xcopy,odx]
override difference between given block size and the block size found by the SCSI READ CAPACITY
command. Use the given block size. Without this flag the copy would not be performed. pt access to
what appears to be a block partition is aborted in version 0.92; that can be overridden by the
force flag. For related reasons the 'norcap' flag requires this flag when applied to a block
device accessed via pt.
xcopy and odx: various limits imposed by associated VPD pages or the RECEIVE COPY OPERATING
PARAMETERS command can be overridden (i.e. exceeded) if this flag is given. Note that the copy
manager will probably object.
fsync [o] [reg,blk]
Flushes data and metadata (describing the file) associated with the OFILE to storage at the end of
the copy.
fua [io] [pt]
causes the FUA (force unit access) bit to be set in SCSI READ and/or WRITE commands. The 6 byte
variants of the SCSI READ and WRITE commands do not support the FUA bit.
fua_nv [io] [pt]
causes the FUA_NV (force unit access non-volatile cache) bit to be set in SCSI READ and/or WRITE
commands. This only has an effect with pt devices. The 6 byte variants of the SCSI READ and WRITE
commands do not support the FUA_NV bit. The FUA_NV bit was made obsolete in SBC-3 revision 35d.
ignoreew [o] [tape]
ignore the early warning indication (of end of tape) when writing to tape. See TAPE section.
immed [io] [odx]
sets the IMMED bit in the POPULATE TOKEN (when [i]) or WRITE USING TOKEN (when [o]) command. That
command should return status promptly after starting the data transfer. The RECEIVE ROD TOKEN
INFORMATION command is then used to poll for completion. SCSI command timeouts should not be
exceeded, even for very large RODs, if this flag is used.
nocache [io] [reg,blk]
use posix_fadvise(POSIX_FADV_DONTNEED) to advise corresponding file there is no need to fill the
file buffer with recently read or written blocks. If used with "iflag=" it will increase the read
ahead on IFILE.
no_del_tkn [o] [odx]
will clear the DEL_TKN bit on the last WRITE USING TOKEN command of each ROD Token in a odx full
copy. In a large odx full copy several ROD Tokens may be used (one after the other). The default
action is to set the DEL_TKN bit on the last WUT command of each ROD. Either way it should not
make much difference because the copy manager deletes a ROD Token when its inactivity time-out
occurs.
nocreat [o]
if OFILE does not exist then an error will be generated rather than creating an empty regular
file. This flag has the same action as "conv=nocreat".
nofm [o] [tape]
no File Mark (FM) on close when writing to tape. See TAPE section.
nopad [o] [tape]
when the block to be written to a tape drive contains less than OBS bytes, then this option causes
the partial block to be written as is. The default action for a tape in this case is to pad the
block. See TAPE section.
norcap [io] [pt]
do not perform SCSI READ CAPACITY command on the corresponding pt device. If used on block device
accessed via pt then 'force' flag is also required. This is to warn about using pt access on what
may be a block device partition.
nowrite [o] [reg,blk,pt]
bypass writes to OFILE. The "records out" count is not incremented. OFILE is still opened but
"oflag=trunc" if given is ignored. Also the ftruncate call associated with the sparse flag is
ignored (i.e. bypassed). Commands such as trim and SCSI SYNCHRONIZE CACHE are still sent.
null [io]
has no affect, just a placeholder.
odx [io] [odx]
indicates to this utility that one of the four variants of an odx copy is requested. Using any of
the --odx, rtf=RTF or rtype=RTYPE options also indicates that odx is requested. See the ODX
section.
pad [o] [reg,blk,pt], [io] [xcopy]
when the block to be written (typically the last block) contains less than OBS bytes, then this
option causes the block to be padded with zeros (i.e. bytes of binary zero). The default action
for a regular file and a fifo is to do a partial write. The default action of a block and a pt
device is to ignore the partial write. The default action of a tape is to pad, so this flag is not
needed (see the nopad flag).
xcopy: sets the PAD bit in the CSCD descriptor of the associated IFILE or OFILE. Is associated
with residual data handling and works together with the cat flag. See the XCOPY section below.
prealloc [o] [reg]
use the fallocate() call prior to starting a copy to set OFILE to its expected size.
prefer_rcs [o] [odx]
prefer RECEIVE COPY STATUS (RCS) command to the RECEIVE ROD TOKEN INFORMATION (RRTI) command which
is the default. This only is active when polling after a WUT command (since polling after a PT
command needs to fetch the ROD Token so it needs the RRTI command).
pt [io] [blk,pt]
causes a device to be accessed in "pt" mode. In "pt" mode SCSI READ and WRITE commands are sent to
access blocks rather than standard UNIX read() and write() commands. The "pt" mode may be implicit
if the device is only capable of passing through SCSI commands (e.g. the /dev/sg* and some
/dev/bsg/* devices in Linux). This flag is needed for device nodes that can be accessed both via
standard UNIX read() and write() commands as well as SCSI commands. Such devices default standard
UNIX read() and write() commands in the absence of this flag.
rarc [i] [pt]
bit set in READ(10, 12, 16 and 32) to suppress RAID rebuild functions when a bad (or recovered
after difficulties) block is detected.
resume [o] [reg]
when a copy is interrupted (e.g. with Control-C from the keyboard) then using the same invocation
again with the addition of "oflag=resume" will attempt to restart the copy from the point of the
interrupt (or just before that point). It is harmless to use "oflag=resume" when OFILE doesn't
exist or is zero length. If the length of OFILE is greater than or equal to the length implied by
a ddpt invocation that includes "oflag=resume" then no further data is copied.
self [io] [pt]
used together with trim flag to do a self trim (trim of segments of a pt device that contain all
zeros). If OFILE is not given, then it is set to the same as IFILE. If SEEK is not given it set to
the same value as SKIP (possibly adjusted if IBS and OBS are different). Implicitly sets "nowrite"
flag.
sparing [o] [reg,blk,pt]
during the copy each IBS * BPT byte segment is read from IFILE into a buffer. Then, instead of
writing that buffer to OFILE, the corresponding segment is read from OFILE into another buffer. If
the two buffers are different, the former buffer is written to the OFILE. If the two buffers
compare equal then the write to OFILE is not performed. Write sparing is useful when a write
operation is significantly slower than a read. Under some conditions flash memory devices have
slow writes plus an upper limit on the number of times the same cell can be rewritten. The
granularity of the comparison can be reduced from the default IBS * BPT byte segment with the the
OBPC value given to the "bpt=" option. The finest granularity is when OBPC is 1 which implies OBS
bytes.
sparse [io] [reg,blk,pt]
after each IBS * BPT byte segment is read from IFILE, it is checked to see if it is all zeros. If
so, that segment is not written to OFILE. See the section on SPARSE WRITES below for the
difference between using this flag once or twice. The granularity of the zero comparison can be
reduced from the default IBS * BPT byte segment with the OBPC value given to the "bpt=" option.
The sparse flag may be used on input when a file is only being read (e.g. when of=OFILE is not
given or OFILE is /dev/null) to determine how many blocks are contained in sparse segments of
IFILE.
ssync [o] [pt]
if OFILE is in "pt" mode then the SCSI SYNCHRONIZE CACHE command is sent to OFILE at the end of
the copy.
strunc [o] [reg]
perform a sparse copy with a ftruncate system call to extend the length of the OFILE if required.
Sets the sparse flag internally if this has not been specified on the command line. See the sparse
flag and the section on SPARSE WRITES below.
sync [io] [reg,blk]
causes the O_SYNC flag to be added to the open of IFILE and/or OFILE. See open(2) man page.
rtf_len [io] [odx]
odx: with the 'read to tokens' variant, after 512 bytes of each ROD Token are written to RTF an
additional 8 byte (big endian) integer is written. That integer is the number of bytes that the
associated ROD represents. The draft standards say for standard ROD types the ROD Token contains
this value. However vendor specific ROD types may be used or vendors may choose not to comply.
Either way the 'write from tokens' variant needs to know the data size associated with the ROD it
is writing from.
trim [io] [pt] [experimental]
similar logic to the "sparse" option. However instead of skipping segments that are full of zeros
a "trim" command is sent to OFILE. Usually set as an oflag argument but for self trim can be used
as an iflag argument (e.g. "iflag=self,trim"). Depending on the usage this may require the device
to support "deterministic read zero after trim". See the TRIM, UNMAP AND WRITE SAME section below.
trunc [o] [reg]
if OFILE is a regular file then it is truncated prior to starting the copy. If SEEK is not given
or 0 then OFILE is truncated to zero length; when SEEK is larger than zero the truncation takes
place at file byte pointer SEEK*OBS. Ignored if "oflag=append". Conflicts with "oflag=sparing".
unmap [io] [pt]
same as the trim flag.
wverify [o] [pt]
this causes SCSI WRITE AND VERIFY commands to be sent to OFILE (instead of SCSI WRITE (or WRITE
ATOMIC) commands). Note that the fua flag is ignored when this flag is given. The BYTCHK field in
the SCSI WRITE AND VERIFY commands is set to zero unless the bytchk flag is also given.
wstream [o] [pt]
this causes SCSI WRITE STREAM(16) command to be sent to OFILE (instead of SCSI WRITE. The Stream
Identify (valid range: 1 to 0xffff (65535)) should be given via the list_id=LID operand (note that
it defaults to 0 which is invalid). The stream can be created (closed (for write) or its status
checked) with the sg_stream_ctl utility. It is the user's responsibility to open a stream before
calling "ddpt ... oflag=wstream list_id=<strm_id>" and close it after, if required.
xcopy [io] [pt]
invoke SCSI XCOPY(LID1) logic and send the XCOPY command to the either IFILE or OFILE depending on
which flag this called. If both are given (i.e. an invocation including 'iflag=xcopy
oflag=xcopy') then send the XCOPY(LID1) to OFILE.
COUNT
When the count=COUNT option is not given (or COUNT is '-1') then an attempt is made to deduce COUNT as
follows.
When both or either IFILE and OFILE are block devices, then the minimum size, expressed in units of input
blocks, is used. When both or either IFILE and OFILE are pass-through devices, then the minimum size,
expressed in units of input blocks, is used.
If a regular file is used as input, its size, expressed in units of input blocks (and rounded up if
necessary) is used. Note that the rounding up of the deduced COUNT may result in a partial read of the
last input block and a corresponding partial write to OFILE if it is a regular file. After a regular file
to regular file copy the length of OFILE will be the same as IFILE unless OFILE existed and its length
was already greater than that of IFILE. To get a copy like the standard Unix cp command, use oflag=trunc
with ddpt.
The size of pt devices is deduced from the SCSI READ CAPACITY command. Block device sizes (or their
partition sizes) are obtained from the operating system, if available.
If skip=SKIP or seek=SEEK are given and the COUNT is deduced (i.e. not explicitly given) then that size
is scaled back so that the copy will not overrun the file or device.
If COUNT is not given and IFILE is a fifo (and stdin is treated as a fifo) then IFILE is read until an
EOF is detected. If COUNT is not given and IFILE is a /dev/zero (or equivalent) then zeros are read
until an error occurs (e.g. file system full).
If COUNT is not given and cannot be deduced then an error message is issued and no copy takes place.
JOB FILES
Some operands can have long arguments (e.g. skip=SKIP and iflag=FLAGS) so that the command line can
become quite long. Also scatter gather lists can be arbitrarily long and may be generated by a program;
then it would be tiresome and error-prone to re-type them on the command line. So the job file was
introduced to hold this utility's operands and options.
A job file is invoked by either the --job=JF option or by placing the job filename (JF) unadorned on the
command line. The job filename cannot contain a "=", start with a hyphen nor be called "ddpt". It is
parsed when it is detected, in a left to right scan of the command line. The JF file must contain the
string "ddpt" and may invoke other job files (to a maximum depth of 4). A job file should not invoke
itself. Also the first line of the job file should not contain any characters (bytes) with their top bit
set; in other words it should be restricted to 7 bit ASCII (otherwise sanity checks might think it is a
binary file and reject it).
The operands and options within a job file are processed in the order they are found (i.e. parsing lines
left to right, top (of file) to bottom). The operands and options may contradict (and cause a syntax
error), override or accumulate with earlier ones, the same as if they appeared on the command line. For
example '-v' on the command line followed by a job file containing '-vv' will result in a verbosity level
of '-vvv' during the copy phase. Empty lines, lines only containing whitespace(s) and anything from and
including a '#' in a job file line are ignored.
SCATTER GATHER LISTS
Each element of a scatter gather list (sgl, plural: sgl_s) is made up of a starting logical block address
(LBA, plural: LBAs), and a number of blocks (NUM) to be accessed from that starting LBA.
The skip=SKIP and seek=SEEK options (and their aliases) can take scatter gather lists. These can be
explicit on the command line, fed in through stdin or in a file whose name is prefixed by "@" or "H@" on
the command line. For large scatter gather lists, placing them in a file is the most practical as command
lines are limited in length. Scatter gather list (sgl) is a collective term for either a scatter list or
a gather list. The actual implementation of each sgl is an array. Syntactically a scatter list and a
gather list are the same.
Conceptually these sgl_s refer to what happens at the "far end" (e.g. within a hard disk or SSD), not
what happens in the computer's memory. So a gather list is associated with the read part of a copy (i.e.
the first half) where a list of Logical Blocks (LBs, identified by their addresses, hence LBAs) and a
number of consecutive, following blocks are "gathered" from the medium (e.g. a SSD). They are formed into
a linear sequence of bytes that is transferred into a segment in the computer's RAM. The second half of
the copy, the write part, may use a scatter list. A scatter list starts with a linear sequence of bytes,
taken from the segment, that is transferred to the device and then "scattered" on the medium as indicated
by the list of LBA,NUM pairs.
In the simplest case a sgl is given on the command line and has the form:
LBA1,NUM1[,LBA2,NUM2[,LBA3,NUM3...]]. There must be an even number of items (i.e. for every LBAn there
should be a following NUMn) with one exception: when LBA1 alone is given, in which case the value 0 is
assumed for NUM1. Comma is the simplest separator for the command line, but whitespace may also be used
(but needs to be escaped because the shell usually interprets whitespace as an option separator). In a
file (or read from stdin or file redirection) more flexibility is permitted in the format. The LBA,NUM
pairs could all appear on one line in a file but the line length is limited to 1024 characters (with a
maximum of 256 parseable items on it). So for longer sgl_s one pair per line is recommended in file
format. Also in file format everything from and including '#' to the end of that line is ignored as are
lines that are empty or only contain whitespace(s).
Each pair becomes one element (or more, see below) of the sgl. By default all numbers given for LBA and
NUM items are in decimal with optional suffix multipliers. Hex numbers use either a "0x" prefix or a 'h'
suffix (hex notation and suffix multipliers cannot be mixed). In the case of a 'H@' lead-in to the
filename on the command line, all numbers are interpreted as hex with no suffix multipliers permitted.
Further, with the 'H@' lead-in the file may contain the string 'HEX' before any numbers are given. The
'HEX' is ignored. The point of this is to catch when a sgl file with default hexadecimal numbers is given
without the 'H@' lead-in; in this case this utility will exit saying that file is in the wrong format.
This "wrong format" action can be bypassed with the --flexible option.
Allowing sgl_s brings lots of flexibility (including the possibility to use the SCSI WRITE SCATTERED
command) but with that comes complexity. Every sgl is scanned to determine if it is monotonic and whether
it has overlapping elements. The term monotonic is used to indicate whether each LBA is in ascending
order, with each LBA greater than the previous element's LBA. Overlapping refers to the situation when
any element's LBA range intersects with any other element's range. Elements that have zero number of
blocks (described here as "degenerate") are ignored for determining monotonic and overlapping (and the
lowest LBA). Overlapping elements are not ideal (but not necessarily fatal). The above mentioned WRITE
SCATTERED command allows the medium's logic to write elements in any order it prefers. That means if
elements overlap, then the user doesn't know which one gets written last (overwriting the one written to
the same LBA earlier). Determining whether element ranges overlap is difficult in the general case (so
this utility doesn't do it) but easy in the case of a monotonic sgl (so this utility does do it).
Warnings are issued in dangerous situations, with the force flag allowing the warning to be overridden.
A degenerate sgl element is one that has zero in its NUM field. Normally degenerate elements are ignored
with some exceptions. The definition of the SCSI WRITE SCATTERED command clearly states that degenerate
elements are valid, thus do not cause an error, but cause no associated action. This utility uses the
concept of a 'hard' and 'soft' sgl: a 'soft' sgl is one in which the last element's NUM is zero (i.e.
its last element is degenerate). A sgl with a non-zero NUM in its last element is considered 'hard'. In a
'soft' sgl the LBA of the last element should be greater than or equal to any LBA+NUM of earlier
elements. Because this is hard to check it is not enforced, so the decision is made on whether a sgl is
hard or soft simply by checking the NUM of that last element. The difference between a hard and soft sgl
is the way the sum of NUM of all elements is used by this utility. For a 'hard' sgl that sum is used for
COUNT when the count=COUNT option is not given; and if count=COUNT is given and the counts differ then
those two values are output and this utility exits with a syntax error. For a 'soft' sgl the degenerate
last element is interpreted as "from the highest LBA in the list to the end of the copy" where the COUNT
is determined some other way. The "highest LBA" is calculated from all elements that have a non-zero
number of blocks plus the LBA of the last element (regardless of whether it is degenerate or not).
The rules in the above paragraph make a one item skip or seek argument (e.g. skip=0x123) in this utility
first become a one element sgl (e.g. containing the pair [0x123, 0x0]). Since this is the last element,
it is a soft sgl and the transfer will start from the given lba (i.e. 0x123) and continues for the number
of blocks indicated by some other mechanism (e.g. an option such as count=COUNT or the length of IFILE).
This mirrors what the classic dd command does with its skip= and seek= options.
Some sgl implementation details: LBAs are stored in 64 bit integers which is more than sufficient to span
even the largest disk array behind a logical device, even if the block size is one byte, which is
unlikely. The NUM field is a 32 bit integer and this is more problematic. The reason is that SCSI WRITE
commands (and their variants) only allocate at most a 32 bit integer for this value. Further, modern
operating systems do not allow any driver to get large amounts of contiguous system RAM, even if the
machine has it available. A 32 bit integer for NUM with each block at 512 bytes is around 2 TB of
storage. Unix system calls (in Linux) also limit each read(2) and write(2) system call to 32 bits of
single bytes which is 4 GB. The problem for this utility is that the NUM can easily exceed 32 bits when a
single scatter gather list element refers to the whole device. The action taken by this utility is to
allow larger than 32 bit NUM values to be given on the command line (or in a scatter gather list file).
However such a large element will be split into multiple elements internally. This will be visible to the
user when the verbose=VERB option (or one of its variants) is used with an elevated value.
There is a helper utility called ddpt_sgl in this package for generating, manipulating and checking
scatter gather lists. See its manpage.
SANITY CHECKS
With powerful data tools, the ability to accidentally overwrite and hence lose important data is ever
present. So a significant portion of the code is dedicated to checking the input arguments for
duplications and contradictions. Still nothing is better than re-reading the command line (which can be
quite long) before hitting the enter key.
Other useful possibilities are to use job files (see the JF argument and the --job=JF option) and the
--dry-run option. The "dry run" option is becoming popular in modern command line utilities and more or
less does what the user would expect. Firstly it parses all the command line arguments then opens IFILE,
OFILE and OFILE2 as directed by the command line and does any meta-data operations that it would
typically do (e.g. check a pass-though or block device's logical block size and object if it differs from
BS, IBS or OBS (whichever applies)). Then just at the point where the code would commence the actual copy
(or read) it does a premature exit. If the --dry-run option is given twice, the code continues into the
copy logic and bypasses the low level read and write calls (and file repositioning). That inner level of
"dry run" is useful for debugging and can be used with multiple verbose=VERB options.
The verbose=VERB option sends diagnostic messages to stderr. The higher value of VERB (in verbose=VERB)
or the more times that -v is used, the greater the volume of diagnostic messages. When use three or more
times then diagnostic messages are generated for each read to, and write from, the working copy buffer;
so the volume of messages is proportional to the number of reads and writes that are done; this can
easily be in the megabyte range. If used less than three times, the reads and writes associated with the
copy do not generate diagnostic messages (unless abnormal situations are encountered). These diagnostic
messages are mainly associated with command line parsing and fetching meta-data about the given files,
plus messages from the cleanup at the end of the copy.
The following command line arguments are checked that they don't appear more than once: bpt=BPT[,OBPC],
bs=BS, count=COUNT, ibs=IBS, if=IFILE, iseek=SKIP, obs=OBS, of=OFILE, of2=OFILE2, oseek=SEEK, seek=SEEK
and skip=SKIP. On the other hand, some arguments are additive, for example iflag=FLAGS, oflag=FLAGS,
status=STAT and --verbose and may appear as many times as required.
XCOPY
This section describes XCOPY(LID1) support with this utility. For ODX support (XCOPY(LID4) subset) see
the ODX section.
A device (logical unit (LU)) that supports XCOPY operations should set the 3PC field (3PC stands for
Third Party Copy) in its standard INQUIRY response. That is not checked when this utility does an xcopy
operation but if it fails, that is one thing that the user may want to check.
If the xcopy starts and fails while underway, then 'sg_copy_results -s' may be useful to view the copy
status. It might also be used from a different process with the same I_T nexus (i.e. the same machine) to
check status during an xcopy operation.
The pad and cat flags control the handling of residual data. As the data can be specified either in terms
of source or target block size and both might have different block sizes residual data is likely to
happen in these cases. If both block sizes are identical these bits have no effect as residual data will
not occur.
If neither of these flags are set, the EXTENDED COPY command will be aborted with additional sense
'UNEXPECTED INEXACT SEGMENT'.
If only the cat flag is set the residual data will be retained and made available for subsequent segment
descriptors. Residual data will be discarded for the last segment descriptor.
If the pad flag is set for the source descriptor only, any residual data for both source or destination
will be discarded.
If the pad flag is set for the target descriptor only any residual source data will be handled as if the
cat flag is set, but any residual destination data will be padded to make a whole block transfer.
If the pad flag is set for both source and target any residual source data will be discarded, and any
residual destination data will be padded.
There is a web page discussing ddpt, XCOPY and ODX at https://sg.danny.cz/sg/ddpt_xcopy_odx.html
ODX
This section describes ODX support (an XCOPY(LID4) subset) for this utility. ODX descriptions use the
following command name abbreviations: PT for the POPULATE TOKEN command, RRTI for the READ ROD TOKEN
INFORMATION command, and WUT for the WRITE USING TOKEN command.
A device (logical unit (LU)) that supports ODX operations is required to set the 3PC field (3PC stands
for Third Party Copy) in its standard INQUIRY response and support the Third Party Copy VPD page. If this
utility generates errors noting the absence of these then the device in question probably does not
support ODX.
There a four variants of ODX supported by ddpt:
full copy : ddpt --odx if=/dev/sg3 bs=512 of=/dev/sg4
zero output blocks : ddpt if=/dev/null rtype=zero bs=512 of=/dev/sg4
read to tokens : ddpt if=/dev/sg3 bs=512 skip=@gath.lst rtf=a.rt
write from tokens : ddpt rtf=a.rt bs=512 of=/dev/sg4 seek=@scat.lst
The full copy will call PT and WUT commands repeatedly until the copy is complete. More precisely the
full copy will make the largest single call to PT allowed by the input's Third Party Copy VPD page (and,
if given, allowed by the BPT argument in the bpt=BPT[,OBPC] option). Then one or more WUT calls are made
to write out from the ROD created by the PT step. The largest single WUT call is constrained by the
output's Third Party Copy VPD page (and, if given, allowed by the OBPC argument in the bpt=BPT[,OBPC]
option). This sequence continues until the requested copy is complete.
The zero output blocks variant is a special case of the full copy in which only WUT calls are made. ODX
defines a special ROD Token to zero blocks. That special ROD Token has a fixed pattern (shown in SBC-3)
and does not need to be created by a PT command like normal ROD Tokens.
The read to tokens and the write from tokens variants are designed to be the read (input) and write
(output) sides respectively of a network copy. Each can run on different machines by sending the RTF
file from the machine doing the read to the machine doing the write. The read to tokens will make one or
more PT calls and output the resulting ROD Tokens to the RTF file. RTF might be a regular file or a named
pipe.
All four variants can have the immed flag set. Then the PT and/or WUT commands are issued with the IMMED
bit set and the RRTI command is used to poll for completion. The delay between the polls is as suggested
by the RRTI command (or if no suggestion is made, 500 milliseconds). Either iflag=immed, oflag=immed or
both can be given but are only effective if the corresponding IFILE or OFILE sends a PT or WUT command.
Typically there is no need to give the list_id=LID option. If this option is not given then 257 is
chosen. If that is busy then 258 is tried. That continues until a usable LID is found or 10 LIDs have
been tried. In the latter case ddpt exits with status of 55 (operation in progress). If the user gives
list_id=LID option and LID is busy then ddpt exits with exit status 55.
If the block size of the input and output are different (i.e. IBS is not equal to OBS) then one must be a
multiple of the other. So an input block size of 512 bytes and an output block size of 4096 bytes (or
vice versa) is acceptable.
The four ODX variants are distinguished as follows: if OFILE is a pass-through device, if=/dev/null (or
equivalent) and rtype=zero then the zero output blocks variant is selected. If both IFILE and OFILE are
pass-through devices and there is some indication of an ODX request (e.g. the --odx option), then the
full copy variant is selected. The read to tokens and the write from token variants are indicated by the
absence of either a of=OFILE or a if=IFILE option, respectively, plus the presence of a rtf=RTF option.
The helper utility ddptctl contains options to issue a single PT, RRTI, WUT or COPY OPERATION ABORT
command. It can also issue a series of polling RRTI commands. It can decode information in ROD Tokens
(which is not as informative as it should be) and print the number of blocks and block size of a disk,
plus protection information if available. See ddptctl.
There is a web page discussing ddpt, XCOPY and ODX at https://sg.danny.cz/sg/ddpt_xcopy_odx.html
SPARSE WRITES
Bypassing writes of blocks full of zeros can save a lot of IO. However with regular files, bypassed
writes at the end of the copy can lead to an OFILE which is shorter than it would have been without
sparse writes. This can lead to integrity checking programs like md5sum and sha1sum generating different
values.
This utility has two ways of handling this file length problem: writing the last block (even if it is
full of zeros) or using the ftruncate system call. A third approach is to ignore the problem (i.e.
leaving OFILE shorter). The ftruncate approach is used when "oflag=strunc" while the last block is
written when "oflag=sparse". To ignore the file length issue use "oflag=sparse,sparse". Note that if
OFILE's length is already correct or longer than required, no action is taken.
The support for sparse writing of regular files may depend on the OS, the file system and the settings of
OFILE. POSIX makes few guarantees when the ftruncate system call is used to extend a file's length, as
may occur when "oflag=strunc". Further, primitive file systems like VFAT may not accept sparse writes or
simulate the effect by writing blocks of zeros. The latter approach will defeat any sparse writing
performance gain.
TRIM, UNMAP AND WRITE SAME
This is a new storage feature often associated with Solid State Disks (SSDs) or disk arrays with "thin
provisioning". In the ATA command set (ACS-2) the relevant command is DATA SET MANAGEMENT with the TRIM
bit set. In the SCSI command set (SBC-3) it is either the UNMAP or WRITE SAME command. Note there is no
TRIM command however the term is frequently used in the technical press.
Trim is a way of telling a storage device that blocks are no longer needed. Keeping the pool of
unwritten blocks large is important for the write performance of SSDs and the thrifty use of real storage
in thin provisioned arrays. Currently file systems in recent OSes may issue trims associated with file
deletes. The trim option in ddpt may be useful when a partition or a whole SSD is to be "deleted". Note
that ddpt is bypassing file systems in that it only offers trim on pass-through (pt) devices.
This utility issues SCSI commands to pt devices and for "trim" currently issues a SCSI WRITE SAME(16)
command with the UNMAP bit set. If the pt device is a SSD with a ATA interface then recent versions of
Linux will translate the SCSI WRITE SAME to the ATA DATA SET MANAGEMENT command with the TRIM bit set.
The maximum size of each "trim" command sent is the size of the copy buffer (i.e. IBS * BPT bytes). And
that maximum can be reduced with the OBPC argument of the "bpt=" option.
The trim can be used various ways. One way is a copy where the copy buffer (or some part of it) is
checked for zeros as is done by the sparse oflag. When a zero segment is found, a trim "command" is sent
to the OFILE. For example:
ddpt if=dsk.img bs=512 of=/dev/sdc oflag=pt,trim
The copy buffer is 64 KiB (since BPT and OBPC default to 128 when "bs=512") and it is checked for all
zeros. If it is all zeros then a trim command is sent to the corresponding location of /dev/sdc which is
accessed via the pt interface. If it is not all zeros then a SCSI WRITE command is sent. Another way is
to trim all or part of a disk. To trim a whole disk (i.e. deleting all its data):
ddpt if=/dev/zero bs=512 of=/dev/sdc oflag=pt,trim
A third way is to "self-trim" which is to only trim those parts of a disk that contain segments full of
zeros:
ddpt if=/dev/sdc skip=0x2300 bs=512 iflag=pt,self,trim count=0x1234f0
The "self" oflag automatically sets up the output side of the copy to send trim commands (if required)
back the the same device (i.e. /dev/sdc). If this example was self-trimming a partition then the
partition would start at LBA 0x2300 and be 0x1234f0 blocks long.
Some random product examples: the Intel X25-M G2 SSDs have trim with recent firmware and they do
deterministic read zero after trim. The Seagate Pulsar SSD has an ATA interface which supports the
deterministic reads of zero after the DATA SET MANAGEMENT command with the TRIM option.
NVME SUPPORT
The following information is Linux specific at this time. NVMe devices in Linux have names like
/dev/nvme0, /dev/nvme0n1 and /dev/nvme0n1p3. The first device name is a character device and some "Admin"
commands can be sent to it (e.g. Identify) but no media access commands (which the NVMe specification
calls the "NVM" Command set). The number given is a controller identifier. Storage in NVMe is associated
with namespaces which are numbered within a controller, starting at 1 (e.g. /dev/nvme0n1 is controller 0,
namespace 1). These device nodes are block devices and can be given as IFILE and/or OFILE. The third type
of NVMe device node selects a partition (within a namespace, within a controller). Partition numbers also
start with 1.
By default ddpt will treat the second and third form (of NVMe device nodes) as standard Linux block
devices. So ddpt will act in the same as the dd utility would. In a similar fashion to accessing SCSI
block devices (e.g. /dev/sdc3) get access NVMe block devices the "pt" flag is required, either with
iflag=FLAGS and/or oflag=FLAGS. There is a SCSI to NVMe Translation Layer (SNTL) in the sg3_utils library
which underpins this utility.
DD DIFFERENCES
dd defaults "if=" and "of=" to stdin and stdout respectively. This follows Unix filter conventions.
However since dd and ddpt are often used to read binary data for timing purposes, having to supply
"of=/dev/null" can be easily forgotten. Without it dd will typically spew binary data on the console. So
ddpt has changed its defaults: the "if=IFILE" is now mandatory for direct copies and to read from stdin
"if=-" can be used; "of=OFILE" remains optional but its default changes to "/dev/null" (or "NUL" in
Windows). To send output to stdout ddpt accepts "of=-".
dd truncates OFILE unless "conv=notrunc" is given. When dd truncates, it truncates to zero length unless
SEEK is greater than zero. ddpt does not truncate OFILE by default. If OFILE exists it will be
overwritten. The overwrite starts at block zero unless SEEK or "oflag=append" is given. If OFILE is a
regular file then "oflag=trunc" (or "conv=trunc") will truncate OFILE prior to the copy.
Numeric arguments to ddpt can be given in hexadecimal, either with a leading "0x" or "0X" or with a
trailing "h". Note that dd accepts "0x123" but interprets it as "0 * 123" (i.e. zero). ddpt will also
interpret "x" as multiplies unless the left operand is zero (e.g. "0x123"). So both dd and ddpt will
interpret "skip=2x123" as "skip=246".
Terabyte size disks make it impractical to copy all the data into a single buffer of 512 bytes length
before writing it out. Therefore both dd and ddpt read a relatively small amount of data into a copy (or
transfer) buffer then write it out to the destination, repeating this process until the COUNT is
exhausted.
A major difference in ddpt is the addition of BPT (Blocks Per Transfer) to control the size of the copy
buffer. With dd, IBS is the size of the copy buffer and the unit of SKIP and COUNT. With ddpt, IBS * BPT
is the size of the copy buffer and IBS is the unit of SKIP and COUNT. This allows ddpt to have its IBS
set to the logical block size of IFILE without unduly restricting the size of the copy buffer. And
setting IBS (and OBS for OFILE) accurately is required when the pass-through interface is used since with
the SCSI READ and WRITE commands the logical block size is implicit.
The way dd handles its copy buffer (outlined in SUSv4 description of dd) is relatively complex,
especially when IBS and OBS are different sizes. The restriction that ddpt places on IBS and OBS ( i.e.
(((IBS * BPT) % OBS) == 0) ) means that a single copy buffer can be used since its size is a multiple of
both IBS and OBS. Being able to precisely define the copy buffer size in ddpt makes sparse writing, write
sparing and trim operations simpler to define and the user to control.
ddpt does not support dd's "cbs=" option (conversion block size). If the "cbs=" option is given to ddpt
then it is ignored.
ddpt adds two types of disk to disk, offloaded copies: XCOPY(LID1) first introduced in SPC-2
(standardized in 2001), and ODX which is a subset of XCOPY(LID4) first introduced in SPC-4 draft
(revision 34, 2012).
PROTECTION INFORMATION
This section is about protection information which is typically an extra 8 bytes associated with each
logical block. Those 8 byte are divided into 3 fields: logical block guard (16 bit (2 byte) CRC), logical
block application tag (2 bytes) and the logical block reference tag (4 bytes). The acronym DIF is
sometimes used for protection information.
The feature to read and/or write protection information by using the protect=RDP[,WRP] option is
currently experimental. It should be used with care and may not "play well" with some other features such
as write sparing and sparse writing. It should be used to copy user data plus the associated protection
information to or from a regular file. It could also be used for a device to device copy assuming the
"pt" interface is used for both. Also only modern SCSI disks support protection information.
When RDP or WRP is greater than 0 then a copy with associated protection information is active. In this
state IBS and OBS must be the same and equal to the logical block size of the device(s) formatted with
protection information. If a SCSI disk with 512 byte logical block size has protection information then
the actual number of bytes transferred for each logical block is typically 520 bytes. For such a disk
BS=512 is required even when additional protection information is being transferred.
When protection type 2 is used, the "normal" READ, WRITE and VERIFY SCSI commands are disallowed. In this
context "normal" means the 6, 10, 12, and 16 byte variants. Only READ(32) and WRITE(32) can be used. The
32 byte variants can be selected in this utility by using the operand 'cdbsz=32'.
MULTIPLIERS
By default numeric arguments to options are assumed to be decimal. Almost all numeric arguments to
options (e.g. COUNT in the count=COUNT option) may include one of these multiplicative suffixes: c C *1;
w W *2; b B *512; k K KiB *1,024; KB *1,000; m M MiB *1,048,576; MB *1,000,000 . This pattern continues
for "G", "T" and "P". The latter two suffixes can only be used for 64 bit values. Some numeric arguments
are limited to 32 bit values (e.g. BSin the bs=BS option). Also a suffix of the form "x<n>" multiplies
the leading number by <n>; however the combinations "0x" and "0X" are treated differently, see the next
paragraph. These multiplicative suffixes are compatible with GNU's dd command (since 2002) which claims
compliance with the SI and with IEC 60027-2 standards.
Alternatively numerical values can be given in hexadecimal indicated by either a leading "0x" or "0X", or
by a trailing "h" or "H". When hex numbers are given, suffix multipliers cannot be used.
If a numeric argument is required to fit in 32 bits and is too large then an error is reported. Usually
negative numbers are not permitted but "count=-1" is a special case and means "all available";
"verbose=-1" is another special case.
NOTES
Copying data behind an Operating System's back can cause problems. In the case of Linux, users should
look at this link: https://linux-mm.org/Drop_Caches
This command sequence may be useful:
sync; echo 3 > /proc/sys/vm/drop_caches
A partial write is a write to the OFILE of less than OBS bytes. This typically occurs at the end of a
copy. dd can do partial writes. ddpt does partial writes to regular files and fifos (including stdout).
However ddpt ignores partial writes when OFILE is a block device or a pt device. When ddpt ignores a
partial write, it sends a warning to the console (stderr).
At the end of the copy two lines are reported to the console:
<in_full>+<in_partial> records in
<out_full>+<out_partial> records out
The "records in" line is the number of full input blocks (each of IBS bytes) that have been read plus the
number of partial blocks ( usually less than IBS bytes) that have been read. Following the lead of dd
when 'iflag=coe' is active a block that cannot be read (and has zeros substituted for its output) is
regarded as a partial read. The "records out" line is the number of full output blocks (each of OBS
bytes) that have been written plus the number of partial blocks (usually less than OBS bytes) that have
been written.
Block devices (e.g. /dev/sda and /dev/hda) can be given for IFILE. If neither 'iflag=direct' nor
'iflag=pt' is given then normal block IO involving buffering and caching is performed. If 'iflag=direct'
is given then the buffering and caching is bypassed (this is applicable to both SCSI devices and ATA
disks). When 'iflag=pt' is given SCSI commands are sent to the device which bypasses most of the actions
performed by the block layer. The same applies for block devices given for OFILE.
All informative, warning and error reports are sent to stderr so that dd's output file can be stdout and
remain unpolluted. If no options are given, then no copying (nor reading) takes place and a brief message
is sent to stderr inviting the user to invoke ddpt again but with '--help' option to get the usage
message.
Disk partition information can often be found with fdisk(8) [the "-ul" argument is useful in this
respect]. Also parted(8) can be used like this: 'parted /dev/sda unit s print' .
For pt devices this utility issues SCSI READ and WRITE (SBC) commands which are appropriate for disks and
reading from CD/DVD/BD drives. Those commands are not formatted correctly for tape drives so ddpt cannot
be used on tape drives via a pt device. If the largest block address of the requested transfer exceeds a
32 bit block number (i.e 0xffffffff) then a warning is issued and the pt device is accessed via SCSI
READ(16) and WRITE(16) commands.
The attributes of a block device (e.g. partitions) are ignored when the pt flag is used. Hence the whole
device is read (rather than just the second partition) by this invocation:
ddpt if=/dev/sdb2 iflag=pt of=t bs=512
Assuming /dev/sdb and /dev/sg2 refer to the same device, then after the following two invocations, the
contents of the files "t", "tt" and "ttt" should be same:
ddpt if=/dev/sdb of=tt bs=512
ddpt if=/dev/sg2 of=ttt bs=512
The SCSI READ(32) and WRITE(32) commands are restricted to media that is formatted with protection type
2. This is a T10 restriction.
SIGNALS
The signal handling has been borrowed from GNU's dd: SIGINT, SIGQUIT and SIGPIPE report the number of
remaining blocks to be transferred and the records in + out counts; then they have their default action.
SIGUSR1 (or SIGINFO) causes the same information to be output and the copy continues. All output caused
by signals is sent to stderr.
Like GNU's dd, ddpt respects the signal disposition of "ignored" (SIG_IGN) set by the shell, script or
other program that invokes ddpt. So in that case it will ignore such signals. Further dd ignores SIGUSR1
if the environment variable POSIXLY_CORRECT is set because POSIX defines dd will only act on SIGINFO (and
Linux has no such signal); ddpt ignores the POSIXLY_CORRECT environment variable. As recommended by
Susv3, ddpt does not expect the signal (blocking) mask to be blocking SIGUSR1 (SIGINFO), SIGINT or
SIGPIPE on entry.
Unix system calls that do IO can be interrupted by signal processing, typically returning an EINTR error
number. The dd utility (and many other Unix utilities) restart the IO operation that was interrupted.
While this will work most of the time for disk IO it is problematic for tape drives because the implicit
position pointer on the tape may have moved. So the default (i.e. "intio=0") in this utility is to mask
those signals during IO operations and only check them prior to starting an IO operation. Most low level
IO (e.g. using SCSI command to write to a disk) will timeout if there is a low level error. However NFS
(the Network File System) will potentially wait for a long time (e.g. expecting a network problem will
soon be fixed) and in this case using "intio=1" may be best.
VERIFY
The usual way to check the two disks (or part of the disks) are the same is to move through the segments
to be compared, reading from both and comparing the returned buffers, stopping if there is an in
equality.
This utility takes a different approach that relies on the OFILE being a pass through device. That
pass-through device needs to support the SCSI VERIFY command with the BYTCHK field set to 1. Optionally,
for the --prefetch option to improve performance that pass-through device needs to support the SCSI
PRE-FETCH command with its IMMED bit set.
When the --verify option is given, instead of reading both IFILE and OFILE, only the IFILE is read. Then
the result of that read is sent to the OFILE device as the data-out buffer of a VERIFY(BYTCHK=1) command.
So the comparison is actually done on the OFILE device rather than the host computer's main memory.
If the --prefetch option is also given, then before the IFILE read, a PRE-FETCH(OFILE, IMMED) is sent.
The IMMED bit will make it return more or less immediately. The effect of the PRE-FETCH should be to
bring the contents of the data to be used for the OFILE side of the comparison, into the OFILE device's
cache. And that should make the later VERIFY(BYTCHK=1) command faster.
TAPE
There is support for copies to and from tape drives in Linux. Only the st driver device names can be used
(e.g. /dev/st0 and /dev/nst2). Hence use of Linux pass-through device names (e.g. /dev/sg2) for tape
drives is not supported. On Debian-based distributions, it is suggested that the mt-st package is
installed as it provides a more fully-featured version of the "mt" tape control program.
Tape drives can operate in fixed- or variable-length block modes. In variable-block mode, each write to
the tape writes a single block of that size. In fixed-block mode, each write to the tape must be a
multiple of the previously-selected block size.
The block size/mode can be set with the mt command prior to invoking ddpt. For example:
# mt -f /dev/nst0 setblk 0
sets variable-block mode, and
# mt -f /dev/nst0 setblk 32768
sets fixed-block mode with block size 32768 bytes.
Note that some tape drives support only fixed-block mode, and possibly even only one block size. (For
example, QIC-150 tapes use a fixed block size of 512 bytes.) There may also be restrictions on the block
size, e.g. it may have to be even.
When using ddpt to write to tape, if the final read from the input is less than OBS, it is padded to OBS
bytes before writing to tape to ensure that all blocks of the tape file are the same length. Having a
shorter final block would fail if the drive is in fixed-block mode, and could create interchange
problems. It is common to expect all blocks in a file on tape to be the same length. However, to tell
ddpt to not pad the final block, use 'oflag=nopad'.
The st tape driver normally writes a filemark when the file (e.g. /dev/nst0) is closed. To not have the
filemark written, use 'oflag=nofm'. One use case for that might be if using ddpt several times in
succession to append more data to the same file on tape. In that case it is probably desirable to write
the filemark at the end of the sequence. So either omit 'oflag=nofm' on the last ddpt invocation, or
manually write a filemark using mt after ddpt exits:
# mt -f /dev/nst0 weof 1
For reading from an unknown tape where the block size(s) is not known, read in variable-block mode
specifying a large IBS. The st driver returns a smaller amount of data if the size of the block read is
smaller. Thus a command like:
# ddpt if=/dev/nst0 of=output.bin bs=262144
should read the file from tape regardless of the block size used (assuming no blocks are larger than
256KB). ddpt's verbose option will display what the actual block size(s) is.
ENVIRONMENT VARIABLES
If the command line invocation of an xcopy does not explicitly (and unambiguously) indicate whether the
XCOPY SCSI command should be sent to IFILE (i.e. the source) or OFILE (i.e. the destination) then a
check is made for the presence of the XCOPY_TO_SRC and XCOPY_TO_DST environment variables. If either one
exists (but not both) then it indicates where the SCSI XCOPY command will be sent. By default the XCOPY
command is sent to OFILE.
The ODX write from tokens variant is very complex to implement if the amount of data held in each ROD is
not known. The value should be found in the "number of bytes represented" field in the ROD Token but that
is not well supported yet by vendors. So for such cases, that number can be appended as a big endian 8
byte integer following each ROD Token in the RTF file. The conv=rtf_len will cause that length to be
appended. Specifying that option on each read to tokens and write from tokens invocation can be a
nuisance. Setting the environment variable ODX_RTF_LEN will cause this utility to act as if the
conv=rtf_len option has been given.
Sometimes the default block size of 512 can be a nuisance. This can be overridden by the value associated
with the DDPT_DEF_BS environment variable. If the environment variable is not found, the value cannot be
decoded or is zero or less, then the default block size remains at 512 bytes.
EXIT STATUS
To aid scripts that call ddpt, the exit status is set to indicate success (0) or failure (1 or more).
Note that some of the lower values correspond to the SCSI sense key values. The exit status values are:
0 success. Also conveys boolean true for actions that result in true or false (e.g. sgl equality
tests)
1 syntax error. Either illegal command line options, options with bad arguments or a combination of
options that is not permitted.
2 the device reports that it is not ready for the operation requested. The device may be in the
process of becoming ready (e.g. spinning up but not at speed) so the utility may work after a
wait.
3 the device reports a medium or hardware error (or a blank check). For example an attempt to read a
corrupted block on a disk will yield this value.
5 the device reports an "illegal request" with an additional sense code other than "invalid
operation code". This is often a supported command with a field set requesting an unsupported
capability.
6 the device reports a "unit attention" condition. This usually indicates that something unrelated
to the requested command has occurred (e.g. a device reset) potentially before the current SCSI
command was sent. The requested command has not been executed by the device. Note that unit
attention conditions are usually only reported once by a device.
7 the device reports a "data protect" sense key. This implies some mechanism has blocked writes (or
possibly all access to the media).
9 the device reports an illegal request with an additional sense code of "invalid operation code"
which means that it doesn't support the requested command.
10 the device reports a "copy aborted". This implies another command or device problem has stopped
and copy operation. The EXTENDED COPY family of commands (including WRITE USING TOKEN) may return
this sense key.
11 the device reports an aborted command. In some cases aborted commands can be retried immediately
(e.g. if the transport aborted the command due to congestion).
14 the DEVICE reports a miscompare sense key. VERIFY and COMPARE AND WRITE commands may report this.
15 the utility is unable to open, close or use the given IFILE, OFILE or other file. The given file
name could be incorrect or there may be permission problems. Adding the -v option may give more
information.
20 the device reports it has a check condition but "no sense". It is unlikely that this value will
occur as an exit status.
21 the device reports a "recovered error". The requested command was successful. Most likely a
utility will report a recovered error to stderr and continue, probably leaving the utility with an
exit status of 0 .
24 the device reports a SCSI status of "reservation conflict". This means access to the device with
the current command has been blocked because another machine (HBA or SCSI "initiator") holds a
reservation on this device. On modern SCSI systems this is related to the use of the PERSISTENT
RESERVATION family of commands.
25 the DEVICE reports a SCSI status of "condition met". Currently only the PRE-FETCH command (see
SBC-4) yields this status.
26 the DEVICE reports a SCSI status of "busy". SAM-5 defines this status as the logical unit is
temporarily unable to process a command. It is recommended to re-issue the command.
27 the DEVICE reports a SCSI status of "task set full".
28 the DEVICE reports a SCSI status of "ACA active". ACA is "auto contingent allegiance" and is
seldom used.
29 the DEVICE reports a SCSI status of "task aborted". SAM-5 says: "This status shall be returned if
a command is aborted by a command or task management function on another I_T nexus and the Control
mode page TAS bit is set to one".
31 error involving two or more command line options. Either they contradict or select an unsupported
mode.
32 the is a logic error in the utility. It corresponds to code comments like "shouldn't/can't get
here". Perhaps the author should be contacted.
33 the command sent to device has timed out. This occurs in Linux only; in other ports a command
timeout will appear as a transport (or OS) error.
36 no error has occurred. For actions that result in a boolean, this exit status indicates false.
40 the command sent to a device has received an "aborted command" sense key with an additional sense
code of 0x10. This value is related to problems with protection information (PI or DIF). For
example this error may occur when reading a block on a drive that has never been written (or is
unmapped) if that drive was formatted with type 1, 2 or 3 protection.
48 this is an internal message indicating a NVMe status field (SF) is other than zero after a command
has been executed (i.e. something went wrong). Work in this area is currently experimental.
49 low level driver reports a response's residual count (i.e. number of bytes actually received by
HBA is 'requested_bytes - residual_count') that is too high. So no useful processing can be done
with that response.
50 + <os_error_number>
OS system calls that fail often return a small integer number to help indicate what the error is.
For example in Unix the inability of a system call to allocate memory returns (in 'errno') ENOMEM
which often is associated with the integer 12. So 62 (i.e. '50 + 12') may be returned by a utility
in this case.
90 the flock flag has been given on a device and some other process holds the advisory exclusive
lock.
97 the response to a SCSI command failed sanity checks.
98 the device reports it has a check condition but the error doesn't fit into any of the above
categories.
99 any errors that can't be categorized into values 1 to 98 may yield this value. This includes
transport and operating system errors after the command has been sent to the device.
100 a command received a 'parameter list length error'.
101 a command received 'illegal field in parameter list'. This may occur with an odx copy if some
combination of parameters is illegal or not supported (e.g. iflag=immed).
105 a command received 'operation in progress'. This may occur with an odx copy when the given LID is
already being used by another process (e.g. also using odx) on the same machine. Choose another
LID.
110 a command received 'invalid token operation, cause not reportable'. This may occur with an odx
operation when the given ROD Token is invalid. One reason for that may be the inactivity timeout
has been reached and the copy manager has cancelled the ROD Token.
110 + <asc_23h_ascq_code>
these status values provide more information than exit status 110. See SPC-5 ASC and ASCQ
assignments (currently in Annex F.2), specifically the entries for asc=23h . For example exit
status 112 corresponds to asc=23h, ascq=2h which implies the odx copy manager does not support
copies between LUs in different targets. That is optional; an odx copy manager is required to
support copies between LUs (that are block devices) in the same target.
126 the utility was found but could not be executed. That might occur if the executable does not have
execute permissions.
127 This is the exit status for utility not found. That might occur when a script calls a utility in
this package but the PATH environment variable has not been properly set up, so the script cannot
find the executable.
128 + <signum>
If a signal kills a utility then the exit status is 128 plus the signal number. For example if a
segmentation fault occurs then a utility is typically killed by SIGSEGV which according to 'man 7
signal' has an associated signal number of 11; so the exit status will be 139 .
255 the utility tried to yield an exit status of 255 or larger. That should not happen; given here for
completeness.
EXAMPLES
The examples in this page use Linux device names. For suitable device names in other supported Operating
Systems see this web page: https://sg.danny.cz/sg/device_name.html . The sg3_utils(8) man page in the
sg3_utils package also covers device naming.
ddpt usage looks quite similar to dd:
ddpt if=/dev/sg0 of=t bs=512 count=1MB
This will copy 1 million 512 byte blocks from the device associated with /dev/sg0 (which should have 512
byte blocks) to a file called t. Assuming /dev/sda and /dev/sg0 are the same device then the above is
equivalent to:
dd if=/dev/sda iflag=direct of=t bs=512 count=1000000
although dd's speed may improve if bs was larger and count was suitably reduced. The use of the
'iflag=direct' option bypasses the buffering and caching that is usually done on a block device.
The dd command's bs argument can be thought of as roughly equivalent to ddpt's bs*bpt . dd almost assumes
buffering on a block device and will work as long as bs is a multiple of the actual logical block size.
Since ddpt can work at a lower level in some cases the bs argument must be a disk's actual logical block
size. Thus the bpt argument was introduced to make the copy more efficient. So these two invocations are
roughly equivalent:
dd if=/dev/sda of=t bs=8k count=64
ddpt if=/dev/sda of=t bs=512 bpt=16 count=1k
In both cases the total number of bytes moved is bs*count . And that will be done by reading 8k (8192
bytes) into a buffer then writing out that buffer to the file t. The read write sequence continues until
the count is complete or an error occurs.
The 'of2=' option can save time when the input would otherwise need to be read twice. For example, to
copy data and take a md5sum of it without needing to re-read the data:
mkfifo fif
md5sum fif &
ddpt if=/dev/sg3 iflag=coe of=sg3.img oflag=sparse of2=fif bs=512
This will image /dev/sg3 (e.g. an unmounted disk) and place the contents in the (sparse) file sg3.img .
Without re-reading the data it will also perform a md5sum calculation on the image.
Now we use sparse writing logic to get some idea of how many blocks on a disk are full of zeros. After a
SCSI FORMAT UNIT command or an ATA SECURITY ERASE command a disk may be all zeros.
ddpt if=/dev/sdc bs=512 oflag=sparse
Since no "of=" option is given, output goes to /dev/null so nothing is actually written so the "records
out" will be zero. However there will be a count of "records in" and "bypassed records out". If /dev/sdc
is full of zeros then "records in" and "bypassed records out" will be the same. Since the "bpt=" option
is not given it defaults to "bpt=128,128" so the copy buffer will be 64 KiB and the sparse check for
zeros will be done with 64 KiB (128 block) granularity.
For examples of the trim and self,trim options see the section above on TRIM, UNMAP AND WRITE SAME.
Following is an example run on a Windows OS using the '--wscan' option which shows the available device
names (e.g. PD1) and the associated volume name(s):
ddpt -w
PD0 [C] FUJITSU MHY2160BH 0000
PD1 [DF] WD 2500BEV External 1.05 WD-WXE90
CDROM0 [E] MATSHITA DVD/CDRW UJDA775 CB03
So, for example, volumes D: and F: reside on PhysicalDisk1 (abbreviated to "PD1") which is manufactured
by WD (Western Digital).
Further examples can be found on this web page: https://sg.danny.cz/sg/ddpt.html . There is a text file
containing examples called ddpt_examples.txt in the "doc" directory of this package's distribution
tarball. The ddpt_examples.txt file contains some examples of using job files.
AUTHORS
Written by Doug Gilbert
REPORTING BUGS
Report bugs to <dgilbert at interlog dot com>.
COPYRIGHT
Copyright © 2008-2021 Douglas Gilbert
This software is distributed under the GPL version 2. There is NO warranty; not even for MERCHANTABILITY
or FITNESS FOR A PARTICULAR PURPOSE.
SEE ALSO
This utility has companion/helper utilities ddptctl(8), ddpt_sgl(8)
There is a web page discussing ddpt at https://sg.danny.cz/sg/ddpt.html
The lmbench package contains lmdd which is also interesting. For moving data to and from tapes see dt
which is found at http://www.scsifaq.org/RMiller_Tools/index.html
To change mode parameters that effect a SCSI device's caching and error recovery see sdparm(sdparm)
To verify the data on the media is readable see: sg_verify(sg3_utils)
To scan and repair disk partitions see TestDisk (testdisk).
Additional references: dd(1), open(2), flock(2), sg_xcopy,sg_copy_results, sg_dd(sg3_utils)