HP StorageWorks Application Recovery Manager Administrator's Guide (T4395-96004, February 2008)

Backup
Overview
Chapter 3 37
Snapshot Replica
This type of replica is produced using snapshot technology, provided by
HP StorageWorks Enterprise Virtual Array.
In the case of a snapshot replica, no synchronization is required before
creating the fixed point-in-time copies because a snapshot is a logical
copy of the pointers to the data rather than the data itself. Snapshot
replicas are considered to be created almost instantaneously and are
immediately available for use. However, in some implementations,
background processes may continue for some time afterwards.
A range of snapshot techniques is available, each with its own particular
merits from the storage and data processing points of view. Application
Recovery Manager supports the following snapshot replica types using
the EVA hardware provider:
•Snapshot with pre-allocation of disk space (standard snapshot).
•Snapshot without pre-allocation of disk space (vsnap or Virtually
Capacity-Free Snapshot).
• A full copy of the source volume (original virtual disk), independent of
the original virtual disk ((snap)clone).
You select the replica type in the GUI when creating a backup
specification. However, you can choose only between clone or snapshot
replica type or you select default. If Snapshot (Differential) is
selected, standard snapshots are created by default. To create vsnaps,
configure the hardware provider to create vsnaps prior creating a backup
specification.
If Default is selected, the replica type created will be the one which is
configured in the hardware provider.
Note that for instant recovery, only clone is available.
HP StorageWorks EVA Specifics
Replica Creation and Reuse
A new replica is created and added to the replica set when the specified
Number of replicas rotated is not reached.
The oldest replica in the set is deleted and the new one is created when
the specified Number of replicas rotated is reached.