Re: unexpected XFS SB magic number

[Eric Sandeen <sandeen@sandeen.net>]

Gaspar Bakos wrote:
> Hi, Eric,

> One of the users was running quite memory and disk IO intensive tasks
> past week. This lead to a crash. (I was not around to keep an eye on
> it). The computer rebooted, and few days later another crash, etc.
> Finally, when I returned this week, I found it powered off.
> 
> And then I realized that the sdc1 partition can not be mounted any more.

Well, something put a gpt label on top of your xfs partition... and it 
wasn't xfs :)

>> i also remember something about parted (maybe...) finding a backup gpt
>> signature at the end of a disk, and "helpfully" copying it over the
>> front end if so.  This was a bug.  sgi guys do you remember?
> 
> But for this one has to invoke parted, and commit the operations done,
> am I right?

if I recall, even invoking parted could do this.

> Maybe there is a nasty daemon doing something. The fs was also exported
> as NFS and mounted by two other hosts.
> 
> ---------
> So the questions are:
> - what partition type to choose next time?
> - is there a simpler way of recovery (than xfs_recovery), i.e. the
>   first few bytes of the partition need to be changed back to something
>   XFS magic, and the rest is probably untouched?

i'd google around and find out how big the gpt header is; try to find 
out how much of the front of your partition got clobbered.  that'll give 
a clue as to how much you may have lost.

-Eric