Veritas Volume Manager 4.1 Administrator's Guide (HP-UX 11i v3, February 2007)

Chapter 1, Understanding VERITAS Volume Manager
Volume Snapshots
47
Release 4.0 of VxVM introduced full-sized instant snapshots and space-optimized instant
snapshots, which offer advantages over traditional third-mirror snapshots such as
immediate availability and easier configuration and administration. You can also use a
third-mirror break-off usage model with full-sized snapshots, where this is necessary for
write-intensive applications.
For more information, see the following sections:
◆ “Full-Sized Instant Snapshots” on page 265.
◆ “Space-Optimized Instant Snapshots” on page 267.
◆ “Emulation of Third-Mirror Break-Off Snapshots” on page 268.
“Comparison of Snapshot Features” on page 47 compares the features that are supported
by the three different types of snapshot.
For more information about taking snapshots of a volume, see “Administering Volume
Snapshots” on page 261, and the vxsnap(1M) and vxassist(1M) manual pages.
Comparison of Snapshot Features
The table, “Comparison of Snapshot Features for Supported Snapshot Types” on page 48,
compares the features of the various types of snapshots that are supported in VxVM.
Full-sized instant snapshots are easier to configure and offer more flexibility of use than
do traditional third-mirror break-off snapshots. For preference, new volumes should be
configured to use snapshots that have been created using the vxsnap command rather
than using the vxassist command. Legacy volumes can also be reconfigured to use
vxsnap snapshots, but this requires rewriting of administration scripts that assume the
vxassist snapshot model.
If storage space is at a premium, space-optimized instant snapshots can be configured
with some reduction of supported functionality. For example, space-optimized snapshots
cannot be turned into independent volumes, nor can they be moved into a separate disk
group for off-host processing.