Strange ZFS problem, filesystem claims to be full when clearly not full

[Oliver Fromme]

Torbjorn Kristoffersen wrote:
 > Here's some news, I finally found a file in a user's .spamassassin directory.
 > 
 > $ ls -l .spamassassin/
 > total 39877936
 > -rw-------  1 gg  gg      76546048 Sep 30 01:13 auto-whitelist
 > -rw-------  1 gg  gg            48 Sep 30 01:51 bayes.lock
 > -rw-------  1 gg  gg      20840448 Sep 30 01:13 bayes_seen
 > ----------  1 gg  gg  552902721536 Sep 30 01:52 temp
 > -rw-------  1 gg  gg          1573 Sep 30 07:51 user_prefs
 > 
 > 
 > Now that is an incredibly huge (and invalid) file! Something like
 > 514GB, far more than the size of this ZFS filesystem.
 > I removed it, and there was no visible effect in df.  Some funny
 > business must be happening with spamassassin though,
 > otherwise this strange file would not be so huge.

Probably a so-called sparse file, i.e. a file with "holes"
that don't actually occupy disk space.  "ls -ls" will print
the number of blocks actually allocated to the file on disk.

I once wrote a script that calculates the "sparseness" of
files.  It's designed for UFS/UFS2.  The output will be
inaccurate for ZFS, but it should still give a rough number.

http://www.secnetix.de/olli/scripts/sparsecheck

Best regards
   Oliver

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