Can I use btrfs-restore to restore ceph osds?

Can I use btrfs-restore to restore ceph osds?

[Guido Winkelmann]

Hi,

I'm currently trying to re-enable my experimental ceph cluster that has been 
offline for a few months. Unfortunately, it appears that, out of the six btrfs 
volumes involved, only one can still be mounted, the other five are broken 
somehow. (If I ever use Ceph in production, it's probably not going to be on 
btrfs after this... I cannot recall whether or not the servers were properly 
shut down the last time, but even if not, this is a bit ridiculous.)

I cannot seem to repair the broken filesystem with btrfsck, but I can extract 
data from them with btrfs-restore.

If I want to restore this whole thing, can I just run btrfs-restore to recover 
the files that were on the broken volume, then make a new filesystem on the 
old partition, and finally copy over the directories and file restored by 
btrfs-restore? Or will that lose important information?

	Guido

Re: Can I use btrfs-restore to restore ceph osds?

[Guido Winkelmann]

Am Mittwoch, 9. Mai 2012, 19:15:19 schrieben Sie:
> I'm currently trying to re-enable my experimental ceph cluster that has been
> offline for a few months. Unfortunately, it appears that, out of the six
> btrfs volumes involved, only one can still be mounted, the other five are
> broken somehow. (If I ever use Ceph in production, it's probably not going
> to be on btrfs after this... I cannot recall whether or not the servers
> were properly shut down the last time, but even if not, this is a bit
> ridiculous.)

In case anybody was wondering, the machines were using kernel 3.1.1 when they 
last ran. (And still are, but I'm preparing a newer kernel.) I don't know yet 
what bug has caused this breakage and whether or not it's still present in 
newer kernels.

	Guido

Re: Can I use btrfs-restore to restore ceph osds?

[Tommi Virtanen]

On Wed, May 9, 2012 at 10:15 AM, Guido Winkelmann
<guido-ceph@thisisnotatest.de> wrote:
> I'm currently trying to re-enable my experimental ceph cluster that has been
> offline for a few months. Unfortunately, it appears that, out of the six btrfs
> volumes involved, only one can still be mounted, the other five are broken
> somehow. (If I ever use Ceph in production, it's probably not going to be on
> btrfs after this... I cannot recall whether or not the servers were properly
> shut down the last time, but even if not, this is a bit ridiculous.)
>
> I cannot seem to repair the broken filesystem with btrfsck, but I can extract
> data from them with btrfs-restore.

OSD uses btrfs snapshots internally. Any restore operation would have
to bring the snapshots back exactly as they were, too. It seems
there's a -s option for that, but whether things will work out is hard
to predict.. since it was a test cluster, perhaps you're better off
scrapping the data and setting up a new cluster.