Veritas Volume Manager 5.1 SP1 Administrator"s Guide (5900-1506, April 2011)

Table 1-1

Comparison of snapshot features for supported snapshot types

(continued)

Break-off

(vxassist or

vxsnap)

Space-optimized

instant

(vxsnap)

Full-sized

instant

(vxsnap)

Snapshot feature

YesNoYesCan be moved into separate disk group

from original volume

YesNoYesCan be turned into an independent

volume

YesYesYesFastResync ability persists across

system reboots or cluster restarts

NoNoYesSynchronization can be controlled

YesNoYesCan be moved off-host

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.

FastResync

Note: Only certain Storage Foundation products have a license to use this feature.

The FastResync feature (previously called Fast Mirror Resynchronization or FMR)

performs quick and efficient resynchronization of stale mirrors (a mirror that is

not synchronized). This increases the efficiency of the VxVM snapshot mechanism,

and improves the performance of operations such as backup and decision support

applications. Typically, these operations require that the volume is quiescent,

and that they are not impeded by updates to the volume by other activities on the

system. To achieve these goals, the snapshot mechanism in VxVM creates an exact

copy of a primary volume at an instant in time. After a snapshot is taken, it can

be accessed independently of the volume from which it was taken. In a Cluster

Volume Manager (CVM) environment with shared access to storage, it is possible

to eliminate the resource contention and performance overhead of using a snapshot

simply by accessing it from a different node.

63Understanding Veritas Volume Manager

FastResync