3PAR InForm® OS 2.3.1 Concepts Guide (320-200112 Rev B, February 2010)

10.7
Virtual Copy Snapshots
InForm OS Version 2.3.1 3PAR InForm OS Concepts Guide
10.4 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 3PAR Virtual Copy 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. System-level maximums of total virtual copies that can
be created on a system also apply. Refer to the 3PAR InForm OS Configuration Matrix for
system-level maximum limits on virtual copies.
Virtual copies can be created and managed in groups to reduce the number of management
tasks. You can create a consistent group virtual copies form a list of virtual volumes, and group
virtual copies into autonomic groups that are managed as one virtual copy.
10.4.1 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
NOTE: 3PAR virtual copies are consistent at the 3PAR virtual volume level, but not
at the host file-system or application level. In other words, virtual copies only
preserve the data that was written on the source 3PAR virtual volume before the
virtual copy is created. Virtual copies do not preserve the data that is resident
within the application or file-system buffers and is not flushed to disk before the
virtual copy is created.
3PAR offers optional 3PAR Recovery Manager DBA software to enable
application-level consistent snapshots. Contact 3PAR Customer Support for more
information.