Re: recovering from "rm -rf"

[David Masover <ninja@slaphack.com>]

Hans Reiser wrote:
> David Masover wrote:
> 
> 
>>
>>I'm not sure yet how much I'm willing to pay.  If the Namesys people can
>>help me out, there will certainly be a donation headed their way,
>>
> 
> Nah, for you it is no charge, you have done a lot for us.

What exactly have I done?  I haven't contributed a single line of code,
just ranted on the mailing list for you.

I appreciate it, but I think I will pay you anyway.  $25 for a question
very well answered, and my mother says she'll match it -- which is still
nowhere near what I'd have had to pay to get the other hard drive
repaired.  Does that WorldPay link work?

> Did you try
> what Vitaly advised yet?

Yes, it seems to have worked.  I seem to have all my important files,
except one album of music and the last few episodes of anime -- and I'm
still going through lost+found.  That's really not much of a loss.

By the way, I also discovered a nice trick to avoid making a full disk
backup.  I had a 500 gig RAID array that I was trying to rescue, and the
biggest spare disk I had available was 80 gigs.  So, I used dm_snapshot
to create a writable snapshot, using a loopback file on the 80 gig drive
as the COW device.  I did the fsck on the snapshot, then wrote the
snapshot back to the original device (dd if=snapshot of=orig_device)
once I was sure it worked.  If it hadn't worked, I could have simply
removed the snapshot (dmsetup remove snapshot).

The COW file was a 60 gig sparse file that ended up using only 2 gigs or
so on disk after the fsck.

Be warned, though, that dm_snapshot isn't quite like LVM snapshots, and
only LVM snapshots are documented, while only dm_snapshot will work for
this.  I had to read the source.