VERITAS Storage Foundation 4.1 Intelligent Storage Provisioning Administrator's Guide

Chapter 5, Administering Instant Snapshots

Creating Instant Snapshots

Note Instant snapshots of ISP application volumes in a disk group’s data pool are best created in

clone pools that are also associated with the same disk group. A snapshot of a snapshot does

not have to be in the same clone pool as its parent.

Volume sets can be used in place of volumes with the following vxsnap operations on

instant snapshots: addmir, dis, make, prepare, reattach, refresh, restore,

rmmir, split, syncpause, syncresume, syncstart, syncstop, syncwait,

and unprepare. A snapshot of a volume set must itself be a volume set. A full-sized

instant snapshot of a volume set can be created using a prepared volume set. You cannot use

the nmirrors or plex attributes to specify that existing plexes are to be broken off. See

the chapter “Creating and Administering Volume Sets” in the VERITAS Volume Manager

Administrator’s Guide for more information on creating volume sets.

Note You may need an additional license to use this feature.

VxVM allows you to make instant snapshots of volumes by using the vxsnap command.

A plex in a full-sized instant snapshot requires as much space as the original volume. If you instead

make a space-optimized instant snapshot of a volume, this only requires enough storage to record

the original contents of the parent volume as they are changed during the life of the snapshot.

The recommended approach to performing volume backup from the command line, or from a

script, is to use the vxsnap command. The vxsnap prepare and make tasks allow you to back

up volumes online with minimal disruption to users.

The vxsnap prepare step creates a DCO and DCO volume and associates this with the volume.

It also enables Persistent FastResync on the volume.

The vxsnap make step creates an instant snapshot that is immediately available for making a

backup. After the snapshot has been taken, read requests for data in the original volume are

satisfied by reading either from a non-updated region of the original volume, or from the copy of

the original contents of an updated region that have been recorded by the snapshot.

Note Synchronization of a full-sized instant snapshot from the original volume is enabled by

default. If you specify the syncing=no attribute to vxsnap make, this disables

synchronization, and the contents of the instant snapshot are unlikely ever to become fully

synchronized with the contents of the original volume at the point in time that the snapshot

was taken. If you wish to move an instant snapshot volume to another disk group for export

to another machine for off-host processing, or to turn it into an independent volume, you

must ensure that the snapshot volume has been completely synchronized.

You can immediately retake a full-sized or space-optimized instant snapshot at any time by using

the vxsnap refresh command. If a fully synchronized instant snapshot is required, you must

wait for the new resynchronization to complete.