Hardware manual

11–1
11 Snapshot management
Snapshots greatly simplify and increase the performance of backup and recovery operations.
About snapshots
A snapshot is a point-in-time copy of volume data. Creating snapshots on a regular basis can protect you from data
loss due to mistakes, viruses, or database corruption.
A snapshot represents the contents of a volume at the time of creation. Y
ou can create snapshots of standard
volumes, in addition to template volumes and thin clone volumes.
Creating a snapshot does not prevent access
to a volume, and the snapshot is instantly available to authorized iSCSI
initiators. If you accidentally delete data, you can set a snapshot online and retrieve the data. If a volume is
corrupted, you can restore the volume from a snapshot. You can also clone a snapshot to create a new copy of a
volume.
Restriction: Y
o
u cannot restore a template volume from a snapshot.
To create snapshots of a volume, you must allocate snapsh
ot reserve for the volume. Initially, a snapshot
consumes no space from the snapshot reserve because it shares all data with the volume (sometimes called the base
volume). When the volume changes, the snapshot reserve tracks those changes to maintain the volume contents at
the time of snapshot creation.
Note: If a volume
is offline, all its snapshots are also offline. If you delete a volume, the group deletes all its
snapshots.
Like volumes, snapshots appear on the network as iSCSI targets. All the iSCSI tar
get security mechanisms apply to
snapshots. See iSCSI target security on
page 8-1.
You can access the data in a snapshot by using the
following methods:
• Restore a volume from a snapshot. This operation replaces the volume with the
data that existed at the time you
created the snapshot. See Restoring a volume from a snapshot on page 1
1-9.
• Clone a snapshot. The new volume contains the volume data
that existed at the time you created the snapshot.
See Cloning a snapshot to create a new volume on pa
ge 11-9.
• Set the snapshot online. iSCSI Initiators can access the targ
et in the usual way. See Setting a snapshot online or
offline on page 11-11.
Y
ou can create snapshots of individual volumes or volume collections
. When you perform a snapshot operation on
a volume collection, the group creates a set of snapshots (one for each volume in the collection) called a snapshot
collection. You can also simultaneously create snapshots of multiple volumes that are not in a collection. The
resulting set of snapshots is called a custom snapshot collection.
Use volume schedules to create snapshots or snaps
h
ot collections at a specific time or time interval, such as hourly,
daily or weekly.