Disk Space Accounting for ZFS Snapshots
When you create a snapshot, its disk space is initially shared between the snapshot and the file system, and possibly with previous snapshots. As the file system changes, disk space that was previously shared becomes unique to the snapshot, and thus is counted in the snapshot's used
property. Additionally, deleting snapshots can increase the amount of disk space unique to (and thus used by) other snapshots.
A snapshot's space referenced
property value is the same as the file system's value was when the snapshot was created.
You can identify additional information about how the values of the used
property are consumed. New read-only file system properties describe disk space usage for clones, file systems, and volumes. For example:
$ zfs list -o space -r rpool
NAME AVAIL USED USEDSNAP USEDDS USEDREFRESERV USEDCHILD
rpool 124G 9.57G 0 302K 0 9.57G
rpool/ROOT 124G 3.38G 0 31K 0 3.38G
rpool/ROOT/solaris 124G 20.5K 0 0 0 20.5K
rpool/ROOT/solaris/var 124G 20.5K 0 20.5K 0 0
rpool/ROOT/solaris-1 124G 3.38G 66.3M 3.14G 0 184M
rpool/ROOT/solaris-1/var 124G 184M 49.9M 134M 0 0
rpool/VARSHARE 124G 39.5K 0 39.5K 0 0
rpool/dump 124G 4.12G 0 4.00G 129M 0
rpool/export 124G 63K 0 32K 0 31K
rpool/export/home 124G 31K 0 31K 0 0
rpool/swap 124G 2.06G 0 2.00G 64.7M 0
For a description of these properties, see the used
properties in the
zfs
(8) man page.