Free space in ZFS

John Levine johnl at iecc.com
Fri Jun 15 21:02:41 UTC 2012


I made a three disk zraid ZFS pool yesterday from three new 1 TB
disks, which I'm using for backup.  Then I did a backup and made a zfs
volume.  The free space numbers don't make sense.  This is on 8.3, ZFS
version 15.

# zpool list
NAME      SIZE   USED  AVAIL    CAP  HEALTH  ALTROOT
backup2  2.72T   310G  2.42T    11%  ONLINE  -

Given that it's zraid, the total available space should be a little
under 2TB since the third disk is for parity.  But zpool gives me a
total of 2.72T, as though the third disk was for data.

# zfs list
NAME                USED  AVAIL  REFER  MOUNTPOINT
backup2             206G  1.58T  31.3K  /backup2
backup2/20120615    206G  1.58T   206G  /backup2/20120615

Well, that makes more sense, total is 1.78Tb.

# df -g
Filesystem        1G-blocks Used Avail Capacity  Mounted on
backup2                1618    0  1618     0%    /backup2
backup2/20120615       1825  206  1618    11%    /backup2/20120615

Now the total is 1.82Tb.  Huh?  The backup filesystems are compressed,
but surely they're showing me the actual size, not the uncompressed
size.  Or are they?

R's,
John



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