HP StorageWorks MSA2012i HP StorageWorks 2000 Modular Smart Array Reference Gu - Page 104

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 Snapshot-1 (Wed Jan 18 22:37:17 2006) Snap Pool-1 Snapshot-2 (Fri Jan 20 22:29:27 2006) Figure 3-3 Relationship Between a Master Volume and its Snapshots and Snap Pool 104 HP StorageWorks 2000 Family Modular Smart Array reference guide • August 2008