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

2.9
3PAR Storage Concepts and Terminology
InForm OS Version 2.2.4 3PAR InForm OS Concepts Guide
destination volume must also be a base volume, have a user space size at least as large as the
user space of the base volume being copied, and must not be exported.
See Chapter 8, Virtual Volumes for additional information on physical copies.
2.1.3.3 Virtual Copies
A virtual copy is a copy, or snapshot, of another virtual volume (a base volume, a physical copy,
or a virtual copy) created using copy-on-write techniques. Unlike a physical copy, which is a
duplicate of an entire base volume, a virtual copy records only changes to the parent volume.
This allows an earlier state of the original virtual volume to be recreated by starting with its
current state and rolling back all the changes that have been made since the virtual copy was
created. Thousands of virtual copies of each virtual volume can be created assuming that there
is sufficient storage space.
Virtual copies can be read-only or read/write. The rules governing virtual copies are such that
read-only and read/write copies must alternate--you can only create a read-only copy of a read/
write volume and a read/write copy of a read-only volume. Additionally, a read-only copy can
have only one read/write virtual copy, whereas a read/write virtual copy can have thousands of
read-only copies. Because base volumes can only be read/write, you can only create read-only
copies of a base volume.
See Chapter 8, Virtual Volumes for additional information on virtual copies.
NOTE: With a 3PAR Remote Copy license, physical copies can be copied from one
InServ Storage Server to another using 3PAR Remote Copy. For additional
information, see the 3PAR Remote Copy User’s Guide.
Table 2-1.
If the virtual copy is created directly from a... it only records...
base volume changes made directly to that base volume
virtual copy changes made directly to that virtual copy