Veritas Volume Manager 5.0.1 Administrator's Guide, HP-UX 11i v3, First Edition, November 2009

One type of volume snapshot in VxVM is the third-mirror break-off type. This

name comes from its implementation where a snapshot plex (or third mirror) is

added to a mirrored volume. The contents of the snapshot plex are then

synchronized from the original plexes of the volume. When this synchronization

is complete, the snapshot plex can be detached as a snapshot volume for use in

backup or decision support applications. At a later time, the snapshot plex can be

reattached to the original volume, requiring a full resynchronization of the

snapshot plex’s contents.

See “Traditional third-mirror break-off snapshots” on page 353.

The FastResync feature was introduced to track writes to the original volume.

This tracking means that only a partial, and therefore much faster,

resynchronization is required on reattaching the snapshot plex. In later releases,

the snapshot model was enhanced to allow snapshot volumes to contain more

than a single plex, reattachment of a subset of a snapshot volume’s plexes, and

persistence of FastResync across system reboots or cluster restarts.

See “FastResync” on page 65.

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 the third-mirror break-off usage model with full-sized snapshots,

where this is necessary for write-intensive applications.

See “Full-sized instant snapshots” on page 354.

See “Space-optimized instant snapshots” on page 356.

See “Emulation of third-mirror break-off snapshots” on page 357.

See “Linked break-off snapshot volumes” on page 357.

See “Comparison of snapshot features” on page 64.

See “About volume snapshots” on page 351.

See the vxassist(1M) manual page.

See the vxsnap(1M) manual page.

Comparison of snapshot features

Table 1-1 compares the features of the various types of snapshots that are

supported in VxVM.

Understanding Veritas Volume Manager

Volume snapshots