Ubuntu Manpage: scsi-config - query information from a scsi device with a nice user interface

Provided by: scsitools_0.12-2.2ubuntu1_amd64

NAME

       scsi-config - query information from a scsi device with a nice user interface

SYNOPSIS

       scsi-config [device]

DESCRIPTION

scsi-config queries information from an scsi target with a nice Tcl/Tk user interface. If
you do not specify a device to query, scsi-config calculates a list of available devices
and prompts it to you.

By the nature of a graphical user interface, most things will explain them self.
Basically, scsi-config shows a list of buttons for certain mode pages which you may press.
Those buttons which you can press and the text windows with white backgrounds can be
modified by you and the modifications send back to the device.

In the main window there is a button to instruct the device to save the data in some non
volatile memory (if it supports it). Note that this will instruct the device to save the
Read-Write Error Recovery Page , Disconnect-Reconnect Page , Format Device Page , Caching
Page , and Control Mode Page in its NVRAM. Usually saving even a single of those should
write them all to the NVRAM, but you never know.

You can query the current, the factory default and the values in the NVRAM (which may not
be the current parameters) from the device.

Not all combinations of button toggles or all values are valid. In general, try to set
them and see which values the drive accepts. scsi-config rereads the device configuration
immediately, s.t. you see which values where accepted.

Also note that some disk drives are notched, and that those have an active notch (shown in
the main window) to which all your settings apply (at least those of notched pages, which
are also marked in slate gray). You can select the active notch to which your settings
apply (and to which the values refer) in the Notch Page.

For those devices which do not feature an NVRAM (generally removable media devices) and as
a kind of backup, you can save the current settings to a file. Actually the file will be a
/bin/sh script making the necessary scsiinfo(8) calls to set the saved parameters when
executed.

There is also a nice Overview button which will query many details about the disk geometry
and draw them in a nice picture. This looks esp. nice for drives with many notches, that
is different regions on the disk with different tracks per sector settings. It is also
very useful for notched drives as you can immediately select the mode pages for each
notch.

SOME USAGE GUIDELINES

1. General Warning
Generally, do not modify settings you don't understand. It is useful to know the
SCSI-II specs mentioned below. Some setting may render the device unusable or even
damage it. Usually a power cycle resets the state (if you do not save the weird
settings in the NVRAM). Some settings affecting the assignment of logical sectors
will render the disk unusable until the next low level format.

2. On Write Caching
As an old warning, this does also mean you should not generally switch the write
cache on. At least on those drives where you have a choice at all. Reasons are
twofold:

a) It is a priori unclear when the drive will actually perform the writes. This
is a bad thing when considering shutdown of your machine. On the other hand,
it seems sensible to assume that the drive will immediately write it's cache
to disk when it is idle (after all file systems are unmounted) and due to
the size of the on disk cache this will usually only need a few seconds
after the shutdown (but the drive lamp will usually not glow, as it is
mostly connected to the host adapter (if you have a lamp at all) and it is
not participating).

There is a SCSI command to flush the caches. Linux could call it prior to
shutting down, spinning a disk down. Due to my knowledge this is not yet
done though.

b) As the writes are performed asynchronously, errors are reported
asynchronously. The disk might return an error at some simple read
instruction related to a write which was acknowledged OK several
transactions ago. This generally confuses things and makes interpreting
errors very difficult. Some devices are known/said to not report write
errors in this mode of operation at all.

Just imagine that at the point where a file system is unmounted, or a new
removable media is detected it could tell: Oops, BTW, there was some write
error ago although I told you it was OK already.

Thus, when you run a disk in write cache mode, keep it in mind when weird error
messages occur and give the disk time to flush it's buffers at shutdown. Generally
it would be good if you knew more vendor specific details on how the disk operates
in the write cache mode.

3. Reassigning Bad Blocks Automatically
One of the nice features of SCSI disk is that they allow to remap bad blocks
automatically as they are detected without any user intervention. However, you
actually have to enable this feature! It turned out that you can not generally
assume a disk in this mode. To enable this mode or check the settings, proceed as
follows:

a) Go to the Read-Write Error Recovery Page. AWRE (Automatic Write
Reallocation Enable) and ARRE (Automatic Read Reallocation Enable) buttons
enable the automatic reallocation.

In the same window, you can select the maximal retries performed. EER allows
the disk to do some Early Error Recovery which is fast (but might misdetect
or miscorrect data). A selected DCR button (Disable CoRrection Codes)
disallows the disk to use any error correction codes at all (thus the drive
will have to retry until it performs an error free read).

Usually a sector will be reallocated after even a single read retry or the
given number of failed write retries. When the sector cannot be recovered,
it is reallocated but the data is lost and an error is signalled.

The other buttons there apply to error reporting as well. TB Transmits the
bad Block together with the error, RC Reads Continuous, that is, does not
pause a read operation while retrying or using error code calculations to
recover a bad block (thus may return bad data). PER lets the disk report
even recovered errors (Post ERror), DTE (Disable Transfer on Error) even
breaks a running data transmission when an error is detected.

b) Even when the reallocation is enabled, the disk must actually have some
reserved areas where to remap the bad blocks. The Format Page controls this.
Either a given number of Alternate Sectors Per LUN is set aside for the
whole disk or a given number of tracks is defined to be a zone and for each
zone a number of sectors or tracks is put aside. These alternate data areas
are where bad sectors are remapped.

Note that this page is very likely to apply only to the current notch on a
notched disk device.

If there are no, or not many alternate sectors reserved on your disk, you
must change these settings.

I found that those disks which allow to modify these settings are very often
set to no reserved sectors at all by the vendors, as this increases the
disks capacity. For the sake of stability, you should really modify these
settings.

If you decide to modify the number of alternate sectors, you must

i) Save the parameters to the NVRAM of the disk.

ii) Low-level format the disk drive (and not erase the NVRAM during this
operation).

to make the changes be effective.

c) Esp. when you set the disk to not report recovered errors (or when it is in
a write cache mode or something), and just as a general guideline, keep an
eye on the grown defects list where the disk will report all the remappings
which took place as your disk ages.

The old adventurers guide line applies: Save (Backup) Early, Save (Backup)
Often. Find the right time to replace your disk avoiding too much work
recovering your data.

BUGS

       scsi-config  could  be  enhanced  by  making better use of Tcl/Tk. I learned much about it
       during my work on tk_scsiformat(8) and their would be much room for fixes and enhances. On
       other hand, it fulfils it's purpose as it is quite nicely already.

       As  scsi-config  makes  heavy  use  of  scsiinfo(8) all it's bugs (esp. on defect reading)
       apply.

FILES

       /usr/lib/scsi/cache, /usr/lib/scsi/control, /usr/lib/scsi/disconnect, /usr/lib/scsi/error,
       /usr/lib/scsi/format,  /usr/lib/scsi/generic,  /usr/lib/scsi/inquiry, /usr/lib/scsi/notch,
       /usr/lib/scsi/overview, /usr/lib/scsi/peripheral, /usr/lib/scsi/rigid, /usr/lib/scsi/save-
       changes,  /usr/lib/scsi/save-file,  /usr/lib/scsi/tworands,  /usr/lib/scsi/verify  (Tcl/Tk
       subroutines used by scsi-config).
       /dev/sd*
       /dev/sg*
       /dev/scd*
       /dev/st*
       /dev/nst*
       /dev/rmt*
       /dev/nrmt*

AUTHORS

       Eric Youngdale.
       Michael Weller <eowmob@exp-math.uni-essen.de>, Versions 1.5 & 1.7