HP P6000 Replication Solutions Manager Administrator Guide (T3680-96069, June 2012)

Snapshot types
Snapshot types are defined by how the array allocates space for the snapshot.
• Demand allocated. The array allocates only enough space to store metadata and pointers to
the source data. As the source is overwritten, the array allocates more space and copies the
original data to the snapshot. Use demand-allocated snapshots when less than 10–25% of
the capacity of the source will change over the life of the snapshot.
• Fully allocated. The array allocates only enough space to store metadata and pointers to the
source data, but reserves space equal to the capacity of the source virtual disk. As the source
is overwritten, the array allocates more space and copies the original data to the snapshot.
Use fully allocated snapshots when more than 25% of the capacity of the source will change
over the life of the snapshot.
Snapshot guidelines
Follow these guidelines for using snapshots:
• The array must have an HP P6000 Business Copy license installed.
• The maximum number of snapshots per source varies, based on the array controller software
version. For specifics, see the HP P6000 Enterprise Virtual Array Compatibility Reference,
located at http://www.hp.com/support/manuals. Select Storage Software under Storage.
• A snapshot is created in the same disk group as the source virtual disk.
• The redundancy (Vraid) level of a snapshot must be the same as or lower than the source.
See “Vraid hierarchy and redundancy” (page 17).
• All snapshots of the same virtual disk must be the same type (demand allocated or fully
allocated) and redundancy (Vraid) level.
• If the disk group has insufficient space to increase the capacity of snapshots, the snapshots
will automatically be invalidated, but the source virtual disks will continue accepting requests.
• Snapshots are included in the maximum number of virtual disks per array.
Snapshots cannot be created when the disk to be replicated is:
• A snapshot
• A disk that is the source of a mirrorclone (however, snapshots of a mirrorclone are possible)
• In the process of normalizing (snapclone in progress) or being deleted
• A thin provisioned virtual disk
Snapclones
A snapclone is an independent, point-in-time copy of a virtual disk. It is independent because all
of the data from the source virtual disk is copied to the snapclone. Use snapclones when you need
independent and durable copies; for example, for data mining, data warehousing, or preproduction
testing.
Follow these guidelines for using snapclones:
• The array must have an HP P6000 Business Copy license installed.
• A snapclone can be in a different disk group than the source.
• The redundancy (Vraid) level of a snapclone can be any level relative to the source. See “Vraid
hierarchy and redundancy” (page 17).
• Until a snapclone is normalized, another snapclone of the same source cannot be created.
Local replication concepts 11