mdconfig on ZFS leaks disk space

[Peter Jeremy]

I recently did a quick experiment to create an 8TB UFS filesystem
via mdconfig and after destroying the md and deleting the file,
the disk space used by the md was not returned - even after a
reboot.  Has anyone else seen this?

I was using a 8.1-prelease/amd64 with everything on ZFS v14 and did:

# truncate -s 8T /tmp/space
# mdconfig -a -t vnode -f /tmp/space
# newfs /dev/md0
/dev/md0: 8388608.0MB (17179869184 sectors) block size 16384, fragment size 2048
        using 45661 cylinder groups of 183.72MB, 11758 blks, 23552 inodes.

This occupied ~450MB on /tmp which uses lzjb compression.

# fsck -t ufs /dev/md0
needed ~550MB VSZ and had ~530MB resident by the end.

# mount /dev/md0 /mnt
# df -k /mnt
/dev/md0  8319620678  4 7654051020 0%  2 1075407868    0%   /mnt

I then copied a random collection of files into /mnt, boosting the
size of /tmp/space to ~880MB.

# umount /mnt
# fsck -t ufs /dev/md0
# mdconfig -d -u 0
# rm /tmp/space

At this point, 'df' on /tmp reported 881MB used whilst 'du' on /tmp
report 1MB used.  lsof showed no references to the space.  Whilst
there were snapshots of /tmp, none had been taken since /tmp/space
was created.  I deleted them anyway to no effect.

Rebooting the system had no effect.

I eventually recovered the space by doing a "zfs destroy zroot/tmp"
and re-creating it.  This showed the in the pool increased by exactly
the amount of extraneous space.

-- 
Peter Jeremy
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