VERITAS Volume Manager 3.5 Administrator's Guide (September 2004)

Administering Volumes
Enabling Persistent FastResync on Existing Volumes with Associated Snapshots
Chapter 8290
# 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”
Step 4. Use the following command on the original volume and on each of its
snapshot volumes (if any) to add a DCO and DCO volume.
# vxassist [-g diskgroup] addlog volume logtype=dco \
dcolen=loglen ndcomirror=number [storage_attribute ...]
Set the value of ndcomirror equal to the number of data and snapshot
plexes in the volume.
The ndcomirror 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 plexes in the volume. For example,
specify ndcomirror=3 when adding a DCO to a 3-way mirrored volume. If
a volume has any snapshot plexes, a separate DCO plex must also be
reserved for each of these plexes. These 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 ndcomirror=5 for a volume
with 3 data plexes and 2 snapshot plexes. For a snapshot volume, set the
value of ndcomirror to the number of plexes in the volume.
The value of the dcolen attribute specifies the size of a DCO plex, and
must be a integer multiple of 33 blocks from 33 to 2112 blocks. The
default value is 132 blocks. A larger value requires more disk space, but
the finer granularity provided by the FastResync maps provides faster
resynchronization.
If a snapshot volume is to be moved to a separate disk group (using the
disk group move, split and join feature), you must ensure that the plexes
its DCO volume are not set up on the same physical disk as the plexes of
any volume that is to remain in the original disk group. To ensure this,
specify appropriate storage attributes to define the disks that can and/or
cannot be used. For example, the following command would allow the
DCO plex for the volume SNAP-vol to be set up on disk disk03, but not
on disk01 or disk02: