Veritas Volume Manager 5.0 Administrator's Guide (September 2006)

266 Administering volumes
Preparing a volume for DRL and instant snapshots
See “Enabling FastResync on a volume” on page 282 for information on how to
enable Persistent or Non-Persistent FastResync on a volume.
■ Dirty Region Logs allow the fast recovery of mirrored volumes after a system crash
(see “Dirty region logging” on page 60 for details). These logs are supported either as
DRL log plexes, or as part of a version 20 DCO volume. Refer to the following
sections for information on enabling DRL on a volume:
■ “Adding traditional DRL logging to a mirrored volume” on page 272 describes
how to add DRL log plexes to a volume.
■ “Preparing a volume for DRL and instant snapshots” on page 266 describes how
to configure DRL for a volume using a version 20 DCO volume.
■ RAID-5 logs are used to prevent corruption of data during recovery of RAID-5
volumes (see “RAID-5 logging” on page 50 for details). These logs are configured as
plexes on disks other than those that are used for the columns of the RAID-5 volume.
See “Adding a RAID-5 log” on page 274 for information on adding RAID-5 logs to a
RAID-5 volume.
Preparing a volume for DRL and instant snapshots
Note: This procedure describes how to add a version 20 data change object (DCO) and
DCO volume to a volume that you previously created in a disk group with a version
number of 110 or greater. If you are creating a new volume in a disk group with a version
number of 110 or greater, you can specify the co-creation of a DCO and DCO volume and
enable DRL as described in “Creating a volume with a version 20 DCO volume” on
page 244. If the volume was created in a release prior to VxVM 4.0, use the procedure in
“Upgrading existing volumes to use version 20 DCOs” on page 270.
You need a full VxVM license and a Veritas FlashSnap
TM
or FastResync license to use the
DRL and FastResync features. 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. For more information about snap objects, see “How persistent
FastResync works with snapshots” on page 70. See “Determining the DCO version
number” on page 268 for details of how to determine the version number of a volume’s
DCO.
Use the following command to add a version 20 DCO and DCO volume to a volume:
# vxsnap [-g diskgroup] prepare volume [ndcomirs=number] \
[regionsize=size] [drl=on|sequential|off] \
[storage_attribute ...]
The ndcomirs 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 and
snapshot plexes in the volume. The DCO plexes are used to set up a DCO volume for any