Harddisc rescue
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] [-J jump-after-blocks] input-file output-file
myrescue is a program to rescue the still-readable data from a damaged harddisk. It is similiar in purpose to dd_rescue, but it tries to quickly get out of damaged areas to first handle the not yet damaged part of the disk and return later.
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 can be used in successive runs to concentrate on 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.
Finally, the program has an option to multiply try to read a block before considering it damaged.
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. Or in case you know what you are doing, e.g. if you know that it is the aging of the magnetisation layer that is causing your problem.
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".
-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; 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.
-J jump-after-blocks
Randomly jump across the disc after reading jump-after-blocks blocks. 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.
-h, -?
Display usage information.
Make sure you have sufficient disk space to copy the whole partition (not just the used ammount of data) to plus some space for the block bitmap (1 byte per block).
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.
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!
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 overflows after 128 failed read attempts.
Kristof Koehler <[email protected]>, Peter Schlaile <[email protected]>
dd(1), dd_rescue(no manpage?)
http://www.google.de/search?q=data+recovery
http://myrescue.sourceforge.net/