Hitachi USP V - Copy-on-Write Snapshot operations

Copy-on-Write Snapshot operations
Copy-on-Write Snapshot normally creates virtual volumes for copying on
write without specifying LUNs as S-VOLs. However, to use a Copy-on-Write
Snapshot volume via the host, it is necessary to map the Copy-on-Write
Snapshot S-VOL to a LUN. Therefore, CCI provides a combined command to
enable the user or application to use the same CCI command in order to
maintain ShadowImage compatibility.
Copy-on-Write 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." Copy-on-Write 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. Copy-on-Write Snapshot and
volume mapping is illustrated in
Figure 6-13 Copy-on-Write Snapshot and
volume mapping on page 6-33.
Figure 6-13 Copy-on-Write Snapshot and volume mapping
Copy-on-Write Snapshot volumes
The specifications for Copy-on-Write 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 (Copy-on-Write Snapshot) can be paired: This
depends on P VOL capacity, Copy-on-Write Snapshot pool capacity, and
shared memory capacity on the RAID storage system.
• Duplicated writing mode: Copying on write.
• Number of mirror volumes:
Data replication operations with CCI
6-33
Command Control Interface User and Reference Guide