Recovering data with ddrescue

I had a hard-drive failure some time ago. The drive was in a really bad shape, which meant that restoring the data in place is out of question. I needed a relatively safe way to dump the disk image to another drive and restore the filesystem there. The usual dd(1) did not work because of a huge number of read errors. I found ddrescue(1), which is doing the same thing as dd but it’s way more tolerant to read errors.

After some time I came up with this combo:

ddrescue -fv -c 32 -r 1 -n /dev/sda3 /dev/sdc1 ddrescue-sda3-recovery.log

Let’s dissect it and see what it does:

• /dev/sda3 – Input device it reads data from
• /dev/sdc1 – Output device it writes data to
• ddrescue-sda3-recovery.log – log file that can be used to resume an interrupted dump later
• -n – skip the scrape phase
• -r 1 – how many times will the program try to read the drive if there were some read errors.
• -c 32 – cluster size, the number of sectors to copy at a time
• -f – force overwrite of the output device/file
• -v – verbose mode

There are many more options, which are documented in the manual page. There are no examples of use though.

After a couple of hours or days we get the dump that we can use to restore data. using other tools. In my case I was able to restore part of the filesystem just with fsck.ext4(8). But as usual, YMMV.

Beware: Don’t just blindly copy/paste the command above. Always double-check the devices and files you read from/to so you don’t destroy your data!