Note
The procedure described in this section adds a DCO log volume that has a version 0 layout as introduced in VxVM 3.2. The version 0 layout supports traditional (third-mirror break-off) snapshots, but not full-sized or space-optimized instant snapshots. See Version 0 DCO volume layout and Version 20 DCO volume layout for a description of the differences between the old and new DCO volume layouts.
See Determining the DCO version number for details of how to determine the version number of a volume's DCO.
To put Persistent FastResync into effect for a volume, a Data Change Object (DCO) and DCO volume must first be associated with that volume. When you have added a DCO object and DCO volume to a volume, you can then enable Persistent FastResync on the volume as described in Enabling FastResync on a volume.
Note You need a Veritas FlashSnapTM or FastResync license to use the FastResync feature. Even if you do not have a license, you can configure a DCO object 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.
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:
To upgrade a disk group to the latest version, use the following command:
For more information, see Upgrading a disk group.
# 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"
# 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 size of each plex is 132 blocks. You can use the dcolen
attribute to specify a different size. If specified, the size of the plex must be an integer multiple of 33 blocks from 33 up to a maximum of 2112 blocks.
You can specify vxassist
-style storage attributes to define the disks that can and/or cannot be used for the plexes of the DCO volume. See Specifying storage for version 0 DCO plexes for details.