Virtual Copy Snapshots; Virtual Copy Snapshot Relationships - HP 3PAR StoreServ 7200 2-node Manual

For the maximum number of physical copies that can be created with your specific system
configuration, go to the Single Point of Connectivity Knowledge (SPOCK) website
www.hp.com/storage/spock.
NOTE: If the base volume and destination volume are both Thinly Provisioned Virtual Volumes
(TPVVs), only the space that is actually used is copied. See
information on TPVVs.

Virtual Copy Snapshots

A virtual copy is a snapshot of another virtual volume. You can make virtual copies of base volumes,
physical copies, or other virtual copies. Virtual copies are created using copy-on-write techniques
available only with the HP 3PAR Virtual Copy Software license. Unlike a physical copy which
duplicates the entire base volume, a virtual copy only records the changes to the original volume.
This allows an earlier state of the original volume to be recreated by starting with the current state
and rolling back all of the changes that have been made since the virtual copy was created.
The system allows you to make a maximum of 500 virtual copies of a base volume. Up to 256
virtual copies can be read/write copies. The maximum number of virtual copies that can be created
on a system is determined by the system configuration. For the maximum number of virtual copies
that can be created with your specific system configuration, go to the Single Point of Connectivity
Knowledge (SPOCK) website http://www.hp.com/storage/spock.
Virtual copies can be created and managed in groups to reduce the number of management tasks.
You can create a consistent group of virtual copies from a list of virtual volumes, and group virtual
copies into autonomic groups that are managed as one virtual copy.
NOTE: Virtual copies are consistent at the virtual volume level, but not at the host filesystem or
application level. In other words, virtual copies only preserve the data that was written on the
source virtual volume before the virtual copy is created. Virtual copies do not preserve the data
that is resident within the application or filesystem buffers and is not flushed to disk before the
virtual copy is created.
HP offers optional HP 3PAR Recovery Manager DBA software to enable application-level consistent
snapshots. Contact HP Customer Support for more information.

Virtual Copy Snapshot Relationships

Base volumes are always read/write, but virtual copies can be read/write or read-only. The rules
that govern the relationships between a base volume and its virtual copies are based upon the
difference between read/write and read-only volumes. Read-only and read/write copies must
alternate. You can only make a read-only copy of a read/write volume, and you can only make
a read/write copy of a read-only volume. Since base volumes are always read/write, you can
only create read-only copies of a base volume. See
read-only and read/write virtual copy relationships.
Figure 7 Alternating Read-only and Read/Write Virtual Copies
46 Virtual Volumes
"Overview" (page 7)
Figure 7 (page 46) for an example of alternating
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