HP XP P9500 Storage - Manual (Page 153)

Snapshot operations
Snapshot normally creates virtual volumes for copying on write without specifying LUNs as S-VOLs.
However, to use a Snapshot volume via the host, it is necessary to map the Snapshot S-VOL to a
LUN. Therefore, RAID Manager provides a combined command to enable the user or application
to use the same RAID Manager command in order to maintain Business Copy compatibility.
Snapshot uses two techniques, one called "V-VOL mapping" (or virtual volume mapping) and the
other is "Snapshot using copy on write" or "Copy-on-Write Snapshot." Snapshot volumes are also
put into pooling volumes called a "Snapshot pool," and a Snapshot pool is specified as a pool ID
when a Snapshot is made. Snapshot and volume mapping is illustrated in
Snapshot and volume
mapping (page 153) .
Figure 56 Snapshot and volume mapping
Snapshot volumes
The specifications for Snapshot volumes are:
•
Allowable type of paired volume: The supported volume type is OPEN-V only for P VOL, and
OPEN-0V for S VOL.
•
Number of volumes (Snapshot) can be paired: This depends on P VOL capacity, Snapshot
pool capacity, and shared memory capacity on the RAID storage system.
•
Duplicated writing mode: Copying on write.
•
Number of mirror volumes:
Fast Snap: Up to 1,024 secondary volumes can be defined for each P VOL. ◦
◦ Snapshot: Up to 64 secondary volumes can be defined for each P VOL.
For details on FastSnap or Snapshot specifications such as maximum number of mirrored volumes,
volumes and operations, please see the HP XP P9000 Fast Snap User Guide or HP XP P9000
Snapshot User Guide for your storage system.
Creating a Snapshot pair
The RAID Manager command for creating a Fast Snap or Snapshot pair is the same as for Business
Copy. However, Fast Snap pair can only operate up to 64 S-VOLs. Therefore, use raidcom command
if you want to operate more than 64 S-VOLs.
The RAID storage system determines whether it is a Business Copy pair or a Fast Snap/Snapshot
pair by the attribute of the S-VOL. The RAID storage system also determines whether it is a Fast
Snap pair or a Snapshot pair by the type of the pool to be used.
Snapshot operations 153