Ubuntu Manpage: myrescue - Harddisc Rescue

NAME

       myrescue - Harddisc Rescue

SYNOPSIS

       myrescue  [-b block-size] [-B bitmap-file] [-A] [-S] [-r retry-count] [-f skip-failed] [-s
       start-block] [-e end-block] [-R] [-G good-range] [-F failed-range]  [-T]  [-J  jump-after-
       blocks] [-U usb-device-file] input-file output-file

DESCRIPTION

myrescue is a program to rescue the still-readable data from a damaged harddisk. It is
similar in purpose to dd_rescue, but it can be run in multiple passes and has options to
avoid damaged areas to first handle the not yet damaged part of the disk.

The program tries to copy the device blockwise to a file and keeps a table ("block
bitmap") noting whether a block has been successfully copied, not yet handled or has had
errors. This block bitmap is used in successive passes to only read the not yet rescued
blocks.

The program has a special skip mode to handle read errors. Usually harddisk surface
defects cover more than just one block and continuous reading in defect areas can damage
the surface, the heads and (by permanent recalibration) the drive mechanics. If this
happens, the chances of rescuing the remaining undamaged data drop dramatically. So in
skip mode, myrescue tries to get out of damaged areas quickly by exponentially increasing
the stepsize. The skipped blocks are marked as unhandled in the block bitmap and can be
retried later.

As another alternative, the program can jump around on the disc, trying random blocks to
first get an overview of the damage. In case of regular defects (e.g. an entire failed
head) this can be used to determine the physical disc structure and to avoid these regions
in the first run.

Also there are options to avoid getting close to already recognized defects or stay in the
proximity of good regions.

Finally, the program has an option to multiply try to read a block before considering it
damaged.

NOTE

       This tools is no replacement for a professional data recovery service!  If you do have the
       latter option, don't even think of using myrescue, as it may  further  damage  your  disk.
       This  tool  is provided only for the case that you are absolutely desperate and definitely
       cannot afford a professional data recovery and know what you are doing.

       Data recovery - whether professional or DIY - is always careful  detective  work.  Damaged
       drives  deteriorate  rapidly  and  behave  nondeterministically,  you may not get a second
       chance once you made a mistake. So you have to be fully aware of  what  you're  doing  and
       understand  precisely what's happening. If you are unsure it's probably best to stop right
       now and ask a linux guru for assistance.

       In any case do not expect too much. While  complete  restores  have  been  witnessed,  you
       should  not  take them for granted. A better attitude is to consider your data lost and be
       glad for any survivors that turn up.

       The usual GPL disclaimer applies. Especially the NON-WARRANTY OF FITNESS FOR A  PARTICULAR
       PURPOSE. Don't blame (or sue) me if it fails to recover or further damages your data.

       And  a  final  word  you  probably  don't  want  to hear in this situation: For the future
       consider a routinely backup to avoid a "next time".

OPTIONS

-b block-size
The size of the blocks (in bytes). Set this to your harddiscs error
detection/correction unit size. Usually this is 4096, which happens to be the
default.

-B bitmap-file
The file containing the status table of all blocks. Nice (or frightening...) to
view with hexdump. 01 means OK; 02 means that the block was OK, but took a long
time to read; 00 means not yet done; negative values mean the number of failed read
attempts. If not given, defaults to output-file.bitmap

-A Abort when encountering errors.

-S Activate skip mode: When encountering errors increase the stepsize exponentially
until a readable block is found.

-f skip-failed
Skip blocks that have already had skip-failed failures. Useful to avoid scratching
the same block over and over again.

-r retry-count
The number of times to read a block before it is declared bad for this run. (You
can still retry it on the next run.) Default: 1

-s start-block
The number of the block to start with. Default: 0

-e end-block
The number of the block, where reading stops (not included!). Default: size of
input-file divided by block-size.

-R Reverse reading direction, i.e. from end-block (excluded) to start-block

-G good-range
Only try to read blocks within good-range blocks from an already successfully read
block.

-F failed-range
Extends -f to also skip any block within failed-range blocks of a block to be
skipped as specified by -f.

-T Also avoid blocks, that were successfully read, but took an unusually long time to
read. In case of growing defects, these blocks can mark the boundaries of defective
regions. This options makes -A, -S and -F treat such blocks as defective.

-J jump-after-blocks
Randomly jump across the disc after reading jump-after-blocks blocks in both
directions. This might be useful to scan discs with scattered defects. In jump
mode -S causes myrescue to jump to a new block upon the first failed sector or upon
hitting a sector to be skipped as specified by -f, -G or -F.

-U usb-device-file
(Linux-specific feature) Perform a bus reset for the specified usb-device-file
after every failed read attempt. Certain faulty SD cards will disappear completely
from the bus after a read error occurs and the USB reader has to be reset
completely in order to continue.

-h, -? Display usage information.

RECOMMENDED PROCEDURE

NOTE: In data recovery every case needs special consideration and a specific approach -
mindlessly running procedures is a bad idea. So consider the following an example, keep a
close eye on the process and be prepared to stop and reconsider if anything unusual
happens. And once again: If you are feeling unsure, stop and ask someone experienced for
assistance.

• Make sure you have sufficient disk space for twice the whole partition (complete
partition size, not just the used amount of data) plus some space for the block
bitmap (1 byte per block). Of course this should NOT be on the damaged disc.

• Determine the hardware block size (CRC/ECC unit) of your harddisk. This may be
found out from hdparm, some entries in /proc/ide/hd? or on the web. I have not yet
checked whether this is possible with an ioctl. If you have, please let me know.

• Start a skip mode run with one retry per block to first copy the undamaged area.

• Start a normal run with one retry per block to copy the remaining skipped blocks.
You may try to use -f 1 to skip the damaged blocks from the first run.

• Repeat until the number of errors seems to have converged. Try waiting a couple of
hours between the retries.

• Repeat this with higher retry counts and wait for convergence.

• Make a copy of the rescued data and run fsck on it. The copy is important! Running
fsck is risky if blocks containing filesystem structures (superblocks, directories,
inodes, journal, ...) are missing. Sometimes the well-meant attempt to correct the
filesystem can damage the image file, so always work on a copy.

• Mount the filesystem (if copied to a file: via loopback) and check your data. If
directory information has been destroyed, fsck moves unidentifiable file fragments
to lost+found, so you should also check this location.

It may help to try reading non-defect areas in between to allow the drive to recalibrate.

The developers are glad to hear about your experiences. Please post them to the
Experiences forum on the Sourceforge Project page. Thank you!

KNOWN BUGS

       The  handling  of  the bitmap-file currently relies on the filesystem semantics, that when
       lseek(2) ing beyond the end of file and then writing, the space in between is filled  with
       zero-bytes.

       The block bitmap maxes out after 127 failed read attempts.

AUTHORS

       Kristof        Koehler        <kristofk@users.sourceforge.net>,       Peter       Schlaile
       <schlaile@users.sourceforge.net>