.zfs directory: snapshot: Bad file descriptor

[Olaf Seibert]

On my production system (still 8.1, I haven't had time yet to upgrade to
8.2) I have a ZFS. Nightly I make snapshots of each filesystem in it.
Suddenly, one of the file systems has no snapshots any more:

$ ls -l /tank/vol-fourquid-1/.zfs
ls: snapshot: Bad file descriptor
total 0
$ ls -l /tank/vol-fourquid-1/.zfs/snapshot
ls: /tank/vol-fourquid-1/.zfs/snapshot: Bad file descriptor

Snapshots in other file systems seem ok, for example:

$ ls -l /home/local/.zfs
total 0
dr-xr-xr-x  9 root  wheel  9 Oct 21  2009 snapshot/
$ ls -l /home/local/.zfs/snapshot/
total 32
drwxr-xr-x  48 root  vb  48 Apr 19  2010 friday/
drwxr-xr-x  48 root  vb  48 Apr 19  2010 monday/
drwxr-xr-x  48 root  vb  48 Apr 19  2010 saturday/
drwxr-xr-x  48 root  vb  48 Apr 19  2010 sunday/
drwxr-xr-x  48 root  vb  48 Apr 19  2010 thursday/
drwxr-xr-x  48 root  vb  48 Apr 19  2010 tuesday/
drwxr-xr-x  48 root  vb  48 Apr 19  2010 wednesday/

zpool status thinks all is ok:

$ zpool status
  pool: tank
 state: ONLINE
status: The pool is formatted using an older on-disk format.  The pool can
        still be used, but some features are unavailable.
action: Upgrade the pool using 'zpool upgrade'.  Once this is done, the
        pool will no longer be accessible on older software versions.
 scrub: none requested
config:

        NAME        STATE     READ WRITE CKSUM
        tank        ONLINE       0     0     0
          raidz2    ONLINE       0     0     0
            da0     ONLINE       0     0     0
            da1     ONLINE       0     0     0
            da2     ONLINE       0     0     0
            da3     ONLINE       0     0     0
            da4     ONLINE       0     0     0
            da5     ONLINE       0     0     0

errors: No known data errors

How worried should I be about corruption anyway, say if I unmount and
remount the affected file system?

-Olaf.
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