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Adding a version 0 DCO and DCO volume

The version 0 DCO log volume was 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" on page 68.

See "Version 20 DCO volume layout" on page 68.

See "Determining the DCO version number" on page 263.

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

See "Enabling FastResync on a volume" on page 276.

  Note   You need a 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.

See "How persistent FastResync works with snapshots" on page 69.

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

  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

See "Upgrading a disk group" on page 194.

  1. 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"

Use the following command to 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 and/or cannot be used for the plexes of the DCO volume.

See "Specifying storage for version 0 DCO plexes" on page 338.