3PAR InForm® OS 2.2.4 Concepts Guide (320-200085 Rev B, March 2009)

8.7
Virtual Volume Types and Variations
InForm OS Version 2.2.4 3PAR InForm OS Concepts Guide
8.7.3 Virtual Copies
A virtual copy is a snapshot of another virtual volume (a base volume or another virtual copy)
created using copy-on-write techniques available only with a 3PAR Virtual Copy license.
Unlike a physical copy, which is a duplicate of the entire base volume, a virtual copy only
records the changes to the original volume (that original volume need not be a base 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 storage system allows you to make hundreds of virtual copies of each virtual volume,
assuming that sufficient storage space is allocated when the base volume is created. However,
the rules that govern the relationships between a base volume and its virtual copies are
complex. To learn more, refer to Virtual Copy Relationships on page 8.7.
For instructions on creating a virtual copy, refer to the InForm OS CLI Administrator’s Manual
or the InForm OS Management Console Online Help.
8.7.3.1 Virtual Copy Relationships
Even though it is not necessary to master the rules governing the relationships between virtual
copies, a basic understanding of these rules is useful when working with virtual copies. This
section provides an overview of the principles involved in virtual copy creation.
Whereas base volumes are always read/write, virtual copies can be read-only or read/write. 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.
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 Virtual Copy DBA software to enable application-level
consistent snapshots.