Creating and Destroying ZFS Snapshots
Snapshots are created by using the zfs snapshot command, which takes as its only argument the name of the snapshot to create. The snapshot name is specified as follows:
filesystem@snapname volume@snapname |
The snapshot name must satisfy the naming conventions defined in ZFS Component Naming Requirements.
In the following example, a snapshot of tank/home/ahrens that is named friday is created.
# zfs snapshot tank/home/ahrens@friday |
You can create snapshots for all descendent file systems by using the -r option. For example:
# zfs snapshot -r tank/home@now # zfs list -t snapshot NAME USED AVAIL REFER MOUNTPOINT tank/home@now 0 - 29.5K - tank/home/ahrens@now 0 - 2.15M - tank/home/anne@now 0 - 1.89M - tank/home/bob@now 0 - 1.89M - tank/home/cindys@now 0 - 2.15M - |
Snapshots have no modifiable properties. Nor can dataset properties be applied to a snapshot.
# zfs set compression=on tank/home/ahrens@now cannot set compression property for 'tank/home/ahrens@now': snapshot properties cannot be modified |
Snapshots are destroyed by using the zfs destroy command. For example:
# zfs destroy tank/home/ahrens@now |
A dataset cannot be destroyed if snapshots of the dataset exist. For example:
A dataset cannot be destroyed if snapshots of the dataset exist. For example:
# zfs destroy tank/home/ahrens cannot destroy 'tank/home/ahrens': filesystem has children use '-r' to destroy the following datasets: tank/home/ahrens@tuesday tank/home/ahrens@wednesday tank/home/ahrens@thursday |
In addition, if clones have been created from a snapshot, then they must be destroyed before the snapshot can be destroyed.
For more information about the destroy subcommand, see Destroying a ZFS File System.
Holding ZFS Snapshots
If you have different automatic snapshot policies so that older snapshots are being inadvertently destroyed by zfs receive because they no longer exist on the sending side, you might consider using the snapshots hold feature.
Holding a snapshot prevents it from being destroyed. In addition, this feature allows a snapshot with clones to be deleted pending the removal of the last clone by using the zfs destroy -d command. Each snapshot has an associated user-reference count, which is initialized to zero. This count increases by one whenever a hold is put on the snapshot and decreases by one whenever a hold is released.
In the previous Solaris release, snapshots could only be destroyed by using the zfs destroy command if it had no clones. In this Solaris release, the snapshot must also have a zero user-reference count.
You can put a hold a snapshot or set of snapshots. For example, the following syntax puts a hold tag, keep, on tank/home/cindys/snap@1.
# zfs hold keep tank/home/cindys@snap1 |
You can use the -r option to recursively hold the snapshots of all descendent file systems. For example:
# zfs snapshot -r tank/home@now # zfs hold -r keep tank/home@now |
The above syntax adds a single reference, keep, to the given snapshot or snapshots. Each snapshot has its own tag namespace and tags must be unique within that space. If a hold exists on a snapshot, attempts to destroy that snapshot by using the zfs destroy command will fail. For example:
# zfs destroy tank/home/cindys@snap1 cannot destroy 'tank/home/cindys@snap1': dataset is busy |
If you want to destroy a held snapshot, use the -d option. For example:
# zfs destroy -d tank/home/cindys@snap1 |
Use the zfs holds command to display a list of held snapshots. For example:
# zfs holds tank/home@now NAME TAG TIMESTAMP tank/home@now keep Fri Oct 2 12:40:12 2009 |
# zfs holds -r tank/home@now NAME TAG TIMESTAMP tank/home/cindys@now keep Fri Oct 2 12:40:12 2009 tank/home/mark@now keep Fri Oct 2 12:40:12 2009 tank/home@now keep Fri Oct 2 12:40:12 2009 |
You can use the zfs release command to release a hold on a snapshot or set of snapshots. For example:
# zfs release -r keep tank/home@now |
If the snapshot is released, the snapshot can be destroy with the zfs destroy command. For example:
# zfs destroy -r tank/home@now |
Two new properties identify snapshot hold information:
-
The defer_destroy property is on if the snapshot has been marked for deferred destroy by using the zfs destroy -d command. Otherwise, the property is off.
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The userrefs property is set to the number of holds on this snapshot.
Renaming ZFS Snapshots
You can rename snapshots but they must be renamed within the same pool and dataset from which they were created. For example:
# zfs rename tank/home/cindys@083006 tank/home/cindys@today |
In addition, the following shortcut syntax provides equivalent snapshot renaming syntax as the example above.
# zfs rename tank/home/cindys@083006 today |
The following snapshot rename operation is not supported because the target pool and file system name are different from the pool and file system where the snapshot was created.
# zfs rename tank/home/cindys@today pool/home/cindys@saturday cannot rename to 'pool/home/cindys@today': snapshots must be part of same dataset |
You can recursively rename snapshots with the zfs rename -r command. For example:
# zfs list NAME USED AVAIL REFER MOUNTPOINT users 270K 16.5G 22K /users users/home 76K 16.5G 22K /users/home users/home@yesterday 0 - 22K - users/home/markm 18K 16.5G 18K /users/home/markm users/home/markm@yesterday 0 - 18K - users/home/marks 18K 16.5G 18K /users/home/marks users/home/marks@yesterday 0 - 18K - users/home/neil 18K 16.5G 18K /users/home/neil users/home/neil@yesterday 0 - 18K - # zfs rename -r users/home@yesterday @2daysago # zfs list -r users/home NAME USED AVAIL REFER MOUNTPOINT users/home 76K 16.5G 22K /users/home users/home@2daysago 0 - 22K - users/home/markm 18K 16.5G 18K /users/home/markm users/home/markm@2daysago 0 - 18K - users/home/marks 18K 16.5G 18K /users/home/marks users/home/marks@2daysago 0 - 18K - users/home/neil 18K 16.5G 18K /users/home/neil users/home/neil@2daysago 0 - 18K - |
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