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 version 0 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

To view the details of the DCO object and DCO volume that are associated with a volume, use the vxprint command. The following is partial vxprint output for the volume named vol1 (the TUTIL0 and PUTIL0 columns are omitted for clarity):

TY  NAME         ASSOC        KSTATE    LENGTH   PLOFFS   STATE  ...
v   vol1         fsgen        ENABLED   1024     -        ACTIVE
pl  vol1-01      vol1         ENABLED   1024     -        ACTIVE
sd  disk01-01    vol1-01      ENABLED   1024     0        -
pl  vol1-02      vol1         ENABLED   1024     -        ACTIVE
sd  disk02-01    vol1-02      ENABLED   1024     0        -
dc  vol1_dco     vol1         -         -        -        -
v   vol1_dcl     gen          ENABLED   132      -        ACTIVE
pl  vol1_dcl-01  vol1_dcl     ENABLED   132      -        ACTIVE
sd  disk03-01    vol1_dcl-01  ENABLED   132      0        -
pl  vol1_dcl-02  vol1_dcl     ENABLED   132      -        ACTIVE
sd  disk04-01    vol1_dcl-02  ENABLED   132        0        -

In this output, the DCO object is shown as vol1_dco, and the DCO volume as vol1_dcl with 2 plexes, vol1_dcl-01 and vol1_dcl-02.

If required, you can use the vxassist move command to relocate DCO plexes to different disks. For example, the following command moves the plexes of the DCO volume, vol1_dcl, for volume vol1 from disk03 and disk04 to disk07 and disk08.

# vxassist -g mydg move vol1_dcl \!disk03 \!disk04 disk07 disk08

See the vxassist(1M) manual page.