VERITAS FlashSnap Point-In-Time-Copy Solutions Administrator's Guide

Chapter 2, Setting up Volumes for Instant Snapshots
Preparing a Volume for Instant Snapshot Operations
21
Considerations for Placing DCO Plexes
If you use the vxassist command or the VERITAS Enterprise Administrator (VEA) to create
both a volume and its DCO, or the vxsnap prepare command to add a DCO to a volume, the
DCO plexes are automatically placed on different disks from the data plexes of the parent volume.
In previous releases, version 0 DCO plexes were placed on the same disks as the data plexes for
convenience when performing disk group split and move operations. As the version 20 DCOs in
VxVM 4.0 and later releases support dirty region logging (DRL) in addition to Persistent
FastResync, it is preferable for the DCO plexes to be separated from the data plexes. This improves
the I/O performance of the volume, and provides resilience for the DRL logs.
If you use the vxsnap prepare command to set up a DCO, you must ensure that the disks that
contain the plexes of the DCO volume accompany their parent volume during the move. Use the
vxprint command on a volume to examine the configuration of its associated DCO volume.
“Examples of Disk Groups That Can and Cannot be Split” on page 22 illustrates some instances in
which it is not be possible to split a disk group because of the location of the DCO plexes.
For more information about relocating DCO plexes, see “Preparing a Volume for Instant Snapshot
Operations” on page 18.