Veritas Volume Manager 4.1 Administrator's Guide (HP-UX 11i v3, February 2007)

Adding a Version 0 DCO and DCO Volume
308 VERITAS Volume Manager Administrator’s Guide
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 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 a 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 308 for details.
Specifying Storage for Version 0 DCO Plexes
Note The operations in this section relate to version 0 DCO volumes. They are not
supported for the version 20 DCO volume layout that was introduced in VxVM 4.0.
If the disks that contain volumes and their snapshots are to be moved or split into
different disk groups, the disks that contain their respective DCO plexes must be able to
accompany them. By default, VxVM attempts to place the DCO plexes on the same disks
as the data plexes of the parent volume. However, this may be impossible if there is
insufficient space available on those disks. In this case, VxVM uses any available space on
other disks in the disk group. If the DCO plexes are placed on disks which are used to
hold the plexes of other volumes, this may cause problems when you subsequently
attempt to move volumes into other disk groups.
You can use storage attributes to specify explicitly which disks to use for the DCO plexes.
If possible, specify the same disks as those on which the volume is configured. For
example, to add a DCO object and DCO volume with plexes on mydg05 and mydg06, and
a plex size of 264 blocks to the volume, myvol, in the disk group, mydg, use the following
command:
# vxassist -g mydg addlog myvol logtype=dco dcolen=264 \
mydg05 mydg06