Veritas Volume Manager 5.0.1 Administrator's Guide, HP-UX 11i v3, First Edition, November 2009

■ Version 20 DCO volumes, introduced in VxVM 4.0, combine DRL logging
(see below) and Persistent FastResync for full-sized and space-optimized
instant volume snapshots.
See “Version 20 DCO volume layout” on page 68.
See “Preparing a volume for DRL and instant snapshots” on page 318.
■ Dirty Region Logs let you quickly recover mirrored volumes after a system
crash. These logs can be either DRL log plexes, or part of a version 20 DCO
volume.
See “Dirty region logging” on page 60.
See “Adding traditional DRL logging to a mirrored volume” on page 326.
See “Preparing a volume for DRL and instant snapshots” on page 318.
■ RAID-5 logs prevent corruption of data during recovery of RAID-5 volumes.
These logs are configured as plexes on disks other than those that are used
for the columns of the RAID-5 volume.
See “RAID-5 logging” on page 52.
See “Adding a RAID-5 log” on page 328.
Preparing a volume for DRL and instant snapshots
You can add a version 20 data change object (DCO) and DCO volume to an existing
volume if the disk group version number is 110 or greater. You can also
simultaneously create a new volume, a DCO and DCO volume, and enable DRL as
long as the disk group version is 110 or greater.
See “Determining the DCO version number” on page 321.
See “Creating a volume with a version 20 DCO volume” on page 293.
See “Upgrading existing volumes to use version 20 DCOs” on page 324.
Note: You need a license key to use the DRL and FastResync feature. If you do not
have a license key, you can configure a DCO object and DCO volume so that snap
objects are associated with the original and snapshot volumes. However, without
a license key, only full resynchronization can be performed.
See “How persistent FastResync works with snapshots” on page 69.
To add a version 20 DCO and DCO volume to a volume, use the following command
:
# vxsnap [-g diskgroup] prepare volume [ndcomirs=number] \
[regionsize=size] [drl=on|sequential|off] \
[storage_attribute ...]
Administering volumes
Preparing a volume for DRL and instant snapshots
318