Oracle Solaris ZFS Administration Guide

Displaying and Accessing ZFS Snapshots

You can enable or disable the display of snapshot listings in the zfs list output by using the listsnapshots pool property. This property is enabled by default.

If you disable this property, you can use the zfs list -t snapshot command to display snapshot information. Or, enable the listsnapshots pool property. For example:

# zpool get listsnapshots tank
NAME  PROPERTY       VALUE      SOURCE
tank  listsnapshots  on        default
# zpool set listsnapshots=off tank
# zpool get listsnapshots tank
NAME  PROPERTY       VALUE      SOURCE
tank  listsnapshots  off         local

Snapshots of file systems are accessible in the .zfs/snapshot directory within the root of the file system. For example, if tank/home/ahrens is mounted on /home/ahrens, then the tank/home/ahrens@thursday snapshot data is accessible in the /home/ahrens/.zfs/snapshot/thursday directory.

# ls /tank/home/ahrens/.zfs/snapshot
tuesday wednesday thursday

You can list snapshots as follows:

# zfs list -t snapshot
NAME                        USED  AVAIL  REFER  MOUNTPOINT
pool/home/anne@monday          0      -   780K  -
pool/home/bob@monday           0      -  1.01M  -
tank/home/ahrens@tuesday   8.50K      -   780K  -
tank/home/ahrens@wednesday 8.50K      -  1.01M  -
tank/home/ahrens@thursday      0      -  1.77M  -
tank/home/cindys@today     8.50K      -   524K  -

You can list snapshots that were created for a particular file system as follows:

# zfs list -r -t snapshot -o name,creation tank/home
NAME                  CREATION
tank/home@now         Wed Jun 30 16:16 2010
tank/home/ahrens@now  Wed Jun 30 16:16 2010
tank/home/anne@now    Wed Jun 30 16:16 2010
tank/home/bob@now     Wed Jun 30 16:16 2010
tank/home/cindys@now  Wed Jun 30 16:16 2010

Disk Space Accounting for ZFS Snapshots

When a snapshot is created, 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 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
# zfs list -ro space tank/home
NAME                  AVAIL   USED  USEDSNAP  USEDDS  USEDREFRESERV  USEDCHILD
tank/home             66.3G   675M         0     26K              0       675M
tank/home@now             -      0         -       -              -          -
tank/home/ahrens      66.3G   259M         0    259M              0          0
tank/home/ahrens@now      -      0         -       -              -          -
tank/home/anne        66.3G   156M         0    156M              0          0
tank/home/anne@now        -      0         -       -              -          -
tank/home/bob         66.3G   156M         0    156M              0          0
tank/home/bob@now         -      0         -       -              -          -
tank/home/cindys      66.3G   104M         0    104M              0          0
tank/home/cindys@now      -      0         -       -              -          -

For a description of these properties, see Table 6–1.