ZFS Snapshot problems

[Jeremy Chadwick]

On Sun, Feb 12, 2012 at 08:12:07AM +0000, Matthew Seaman wrote:
> 
> Since about a week ago I've been intermittently getting a problem where
> I cannot access a snapshot after creating it:
> 
> lucid-nonsense:~:# zfs snapshot zroot at test
> lucid-nonsense:~:# zfs list -t snapshot
> NAME         USED  AVAIL  REFER  MOUNTPOINT
> zroot at test    67K      -  8.36G  -
> lucid-nonsense:~:# cd /.zfs/snapshot/test
> /.zfs/snapshot/test: Not a directory.
> 
> This is playing silly buggers with my backups.  Apart from that, the
> system is behaving normally.  Nothing in syslog, nothing in dmesg.
> The only way I've found so far to clear the problem is to reboot, but
> then the problem seems to recur within a few days.
> 
> 'zpool status' says everything is fine. 'zpool scrub' has no effect.
> 
> lucid-nonsense:~:# uname -a
> FreeBSD lucid-nonsense.infracaninophile.co.uk 8.2-STABLE FreeBSD
> 8.2-STABLE #2 r231394: Fri Feb 10 20:35:13 GMT 2012
> root at lucid-nonsense.infracaninophile.co.uk:/usr/obj/usr/src/sys/LUCID-NONSENSE
>  amd64
> lucid-nonsense:~:# zpool upgrade
> This system is currently running ZFS pool version 28.
> 
> All pools are formatted using this version.
> lucid-nonsense:~:# zfs upgrade
> This system is currently running ZFS filesystem version 5.
> 
> All filesystems are formatted with the current version.
> 
> Any clues about how I can debug this, and hopefully prevent it happening?

Could this be related (somehow) to the below commit?  I'm doubting it,
but...

http://www.freebsd.org/cgi/cvsweb.cgi/src/cddl/contrib/opensolaris/cmd/zfs/zfs_main.c

I realise you're not destroying a snapshot, but I wonder if an old
snapshot which was previously destroyed wasn't really destroyed, thus
resulting in the behaviour you see.  As stated, I doubt it, but I
imagine it depends on how this issue manifests itself.

-- 
| Jeremy Chadwick                                 jdc at parodius.com |
| Parodius Networking                     http://www.parodius.com/ |
| UNIX Systems Administrator                 Mountain View, CA, US |
| Making life hard for others since 1977.             PGP 4BD6C0CB |