Using Snapshot Services - HP 2000fc Reference Manual

Using Snapshot Services

Snapshot services provide data protection by enabling you to create and save
snapshots of a volume, where each snapshot preserves the volume's data state at the
point in time when the snapshot was created.
Snapshots can be taken of master volumes only. A master volume is a volume that
has been enabled for snapshots. You can either create a master volume directly or
convert a standard volume to a master volume.
Master volumes are associated with a snap pool, which contains pre-allocated
reserve space for the snapshot data. A snap pool represents the storage area that is to
hold the copy of the data or pointers to the data created by the snapshot. A snap
pool can have 16 associated master volumes. A master volume and its associated
snap pool must be owned by the same controller. Threshold levels and associated
policies specify the action that the storage system takes when the threshold value of
the snap pool is reached.
A snapshot is a virtual volume. While really a set of pointers to a portion of the
snap pool, a snapshot behaves like a volume in that it can be mapped to data hosts
and the mapping can be assigned a LUN and be made accessible as read-only or
read-write, depending on the purpose of the snapshot.
The following figure shows how the data state of a master volume is preserved in
the snap pool by two snapshots taken at different points in time. The dotted line
used for the snapshot borders indicates that snapshots are logical volumes, not
physical volumes as are master volumes and snap pools.
MasterVolume-1
Figure 3-3 Relationship Between a Master Volume and its Snapshots and Snap
104 HP StorageWorks 2000 Family Modular Smart Array reference guide • August 2008
Snapshot-1
(Wed Jan 18 22:37:17 2006)
Snapshot-2
(Fri Jan 20 22:29:27 2006)
Pool
Snap Pool-1