VERITAS FlashSnap Point-In-Time-Copy Solutions Administrator's Guide

Chapter 2, Setting up Volumes for Instant Snapshots

Preparing a Volume for Instant Snapshot Operations

To upgrade a disk group, use the following command:

# vxdg upgrade diskgroup

2. Use the following command to add a version 20 DCO and DCO volume to an existing volume:

# vxsnap [-g diskgroup] prepare volume [ndcomirs=number] \

[regionsize=size] [alloc=storage_attribute[,...]]

The ndcomirs attribute specifies the number of DCO plexes that are created in the DCO

volume. It is recommended that you configure as many DCO plexes as there are data and

snapshot plexes in the volume. The DCO plexes are used to set up a DCO volume for any

snapshot volume that you subsequently create from the snapshot plexes. For example, specify

ndcomirs=5 for a volume with 3 data plexes and 2 snapshot plexes.

The value of the regionsize attribute specifies the size of the tracked regions in the

volume. A write to a region is tracked by setting a bit in the change map. The default value is

64k (64KB). A smaller value requires more disk space for the change maps, but the finer

granularity provides faster resynchronization.

You can also specify vxassist-style storage attributes to define the disks that can and/or

cannot be used for the plexes of the DCO volume.

Note The vxsnap prepare command automatically enables Persistent FastResync on the

volume. Persistent FastResync is also set automatically on any snapshots that are

generated from a volume on which this feature is enabled.

If the volume is a RAID-5 volume, it is converted to a layered volume that can be used

with instant snapshots and Persistent FastResync.

By default, a new-style DCO volume contains 32 per-volume maps. If you require more

maps than this, you can use the vxsnap addmap command to add more maps. See the

vxsnap(1M) manual page for details of this command.

3. If you are going to create a snapshot volume by breaking off existing plexes, use the following

command to add one or more snapshot mirrors to the volume:

# vxsnap [-b] [-g diskgroup] addmir volume [nmirror=N] \

[alloc=storage_attribute[,...]]

By default, one snapshot plex is added unless you specify a number using the nmirror

attribute. For a backup, you should usually only require one plex. The mirrors remain in the

SNAPATT state until they are fully synchronized. The -b option can be used to perform the

synchronization in the background. Once synchronized, the mirrors are placed in the

SNAPDONE state.

For example, the following command adds 2 mirrors to the volume, vol1, on disks mydg10

and mydg11: