VERITAS Volume Manager 3.5 Administrator's Guide (September 2002)

Adding a DCO and DCO Volume

194 VERITAS Volume Manager Administrator’s Guide

Note You mayneed an additional license touse the Persistent FastResyncfeature. Even if

you donot have a license, you can conﬁgure a DCOobject and DCO volume so that

snap objects are associated with the original and snapshot volumes. For more

information about snap objects, see “How Persistent FastResync Works with

Snapshots” on page 45.

To add a DCO object and DCO volume to an existing volume (which may already have

dirty region logging (DRL) enabled), use the following procedure:

1. Ensure that the disk group containing the existing volume has been upgraded to at

least version 90. Use the following command to check the version of a disk group:

# vxdg list diskgroup

To upgrade a disk group to the latest version, use the following command:

# vxdg upgrade diskgroup

For more information, see “Upgrading a Disk Group” on page 133.

2. Use the following command to turn off Non-Persistent FastResync on the original

volume if it is currently enabled:

# vxvol [-g diskgroup] set fastresync=off volume

If you are uncertain about which volumes have Non-Persistent FastResync enabled,

use the following command to obtain a listing of such volumes:

# vxprint [-g diskgroup] -F “%name” \

-e “v_fastresync=on && !v_hasdcolog”

3. Use the following command to add a DCO and DCO volume to the existing volume:

# vxassist [-g diskgroup[ addlog volume logtype=dco \

[ndcomirror=number] [dcolen=size] [storage_attributes]

For non-layered volumes, the default number of plexes in the mirrored DCO volume

is equal to the lesser of the number of plexes in the data volume or 2. For layered

volumes, the default number of DCO plexes is always 2. If required, use the

ndcomirror attribute to specify a different number. It is recommended that you

conﬁgure as many DCO plexes as there are existing data and snapshot plexes in the

volume. For example, specify ndcomirror=3 when adding a DCO to a 3-way

mirrored volume.

The default sizeof eachplex is 132blocks. You canuse thedcolen attribute tospecify

a different size. If speciﬁed, the sizeof the plex must be a integermultiple of33 blocks

from 33 up to a maximum of 2112 blocks.