Adding a version 0 DCO and DCO volume

To put Persistent FastResync into effect for a volume, a data change object (DCO) and DCO volume must be associated with that volume. After you add a DCO object and DCO volume to a volume, you can enable Persistent FastResync on the volume.


You need a FastResync license key 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.

The procedure in this section describes adding a version 0 layout DCO. A version 0 DCO layout supports traditional (third-mirror break-off) snapshots that are administered with the vxassist command. A version 0 DCO layout does not support full-sized or space-optimized instant snapshots.

To add a DCO object and DCO volume to an existing volume

  1. Ensure that the disk group containing the existing volume has at least disk group version 90. To check the version of a disk group:
    # vxdg list diskgroup

    If required, upgrade the disk group to the latest version:

    # vxdg upgrade diskgroup
  2. 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.


    The ! character is a special character in some shells. The following example shows how to escape it in a bash shell.

    # vxprint [-g diskgroup] -F "%name" \
      -e "v_fastresync=on && \!v_hasdcolog"
  3. Add a DCO and DCO volume to the existing volume (which may already have dirty region logging (DRL) enabled):
    # 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 or cannot be used for the plexes of the DCO volume.

More Information

Specifying storage for version 0 DCO plexes