Sunday, April 13, 2008

Rescue data from a reiserfs partition

Couple of days ago, I met a situation, when my /home partition, which was on reiserfs filesystem, all the sudden, got dead. It was not able to restore the partition with reiserfs utils, it didn't want to mount anymore, info said there only 563 Kb of 60 Gb data left. Not good.

I've spent a day rescuing the data, and managed to get back 99% of it (i belive), so now I share the experience.

The rule number one in such a situation is to calm down. Sit down, take a blank sheet of paper, a pencil and then in a nice friendly characters write the phrase "DON'T PANIC".

I'm serious, it's pretty easy to get jumpy and overreactive when "all of yours" suddenly getting disappeared. And surrely it's easy to broke something down completely. So, don't touch anything until you get back to the cool consciousness.

The second thing you need, is a complete copy of your damaged partition. For that you'll need another free partition with exact same size. If you have such space on another hard drive, create it there, or think about baying another one.

Once you have your new partition for the backup. You need to boot up on some kind of live-cd with a linux environment. I've used the ubuntu 7.10 live-cd, it's quite handy, understand most of the modern hardware, contains the gparted util, have a web-browser etc. So it's stuffed pretty good for our purpose.

When you have your live cd booted up, you may copy the partitions. There's a builtin prgramm called 'dd', which allows you to copy block devices byte by byte, one to another. So you run it like that.

$ sudo dd conv=noerror if=/dev/old of=/dev/new

Where the '/dev/old' and '/dev/new' are your damaged and backup partitions. The optional attribute 'conv=noerror' tells the commad to skip reading errors.

Optionally you may unlock the 'universe' repository and install the 'dd_rescue' prgramm, which I belive, a wrapper for the 'dd' command and provides some more resuce oriended functionality.

The main point is to create an exact copy of the aviable data from the damaged partition.

And note, depends on the conditions, this may take quite a long time. My 60G partition was copied in about 7 hours.

That's it. Once you have a copy block. You run the 'reiserfsck' on the _copy_ partition like that.

$ sudo reiserfsck --rebuild-tree -S /dev/new

Note the '-S' option. This tells the reiserfsck programm to scan the whole partition for the aviable data. It's important, don't miss it up.

This operation usually is quite fast. Depends on the size of your data, and its condition this will take some minutes.

After the reiserfsck pargamm have finished, mount your new partition and take a look how is it going. If your partition was not damaged too hard, most of the data and directories structure will be on the right places. And there will be the 'lost+found' directory, take a look in it too, there will be lots of directories and subdirectories named with numbers. The util put there the files which were recovered but which former place was not found. And you may find there some files which you have deleted recently. So browse throw the directories, you may find some valuable data there too.

This is pretty much it. In really it's qute a simple stuff. Just don't get scary, some bad blocks on your hard drive is not a big problem, most of your data usually safe untill the harddrive any-working.

1 comment:

Anonymous said...

Ahtung! 7 hours!!! {shuting in head}
So bad blocks on your hard drive is not a big problem if you file system is reiserfs! but if ext3? need "Buben" now.