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65Understanding Veritas Volume Manager
Volume snapshots
mirror snapshots such as immediate availability and easier configuration and
administration. You can also use the 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 307.
■ “Space-optimized instant snapshots” on page 309.
■ “Emulation of third-mirror break-off snapshots” on page 310.
■ “Linked break-off snapshot volumes” on page 311.
“Comparison of snapshot features” on page 65 compares the features that are
supported by the different types of snapshot.
For more information about taking snapshots of a volume, see “Administering
volume snapshots” on page 303, 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 65, 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.
Table 1-1 Comparison of snapshot features for supported snapshot types
Snapshot feature Full-sized
instant (vxsnap)
Space-
optimized
instant (vxsnap)
Break-off
(vxassist or
vxsnap)
Immediately available for
use on creation
Yes Yes No
Requires less storage
space than original
volume
No Yes No