VERITAS Storage Foundation 4.1 Intelligent Storage Provisioning Administrator's Guide

Creating a Volume for Use with Snapshots and DRL
54 VERITAS Storage Foundation ISP Administrator’s Guide
separateby "Controller"
}
capability ’DataMirroring(nmirs=2)’
}
};
Creating a Volume for Use with Snapshots and DRL
If the dirty region logging (DRL) or instant snapshot features are going to be used with an
application volume, a version 20 data change object (DCO) and DCO volume must be associated
with the volume.
If you want to create a volume of which you can take instant snapshots, the
InstantSnapShottable capability or template must be specified (unless this capability is
already implied by another capability or template):
# vxvoladm -g mydg make mir3vol 1g \
capability=’DataMirroring(nmirs=3),InstantSnapshottable’ \
init=active
By default, a data change object (DCO) and DCO volume with a single plex are associated with a
volume to enable the instant snapshot capability. To increase the redundancy of the DCO volume,
specify the DCOLogMirroring capability as shown here:
# vxvoladm -g mydg make mir3vol 1g \
capability=’DataMirroring(nmirs=3),InstantSnapshottable,\
DCOLogMirroring(nlogs=3)’ init=active
In this example, the same degree of redundancy is created for the DCO volume as for the data
volume.
The DCO and DCO volume that are added by the InstantSnapShottable capability also
provide the dirty region logging (DRL) capability that speeds recovery of mirrored volumes after a
system crash. To enable DRL, specify either the attribute drl=on for full DRL, or
drl=sequential for sequential DRL (used with volumes containing database replay logs). By
default, DRL is disabled (drl=off). For example, the following command enables DRL for the
volume, mir3vol, that is being created:
# vxvoladm -g mydg make mir3vol 1g \
capability=’DataMirroring(nmirs=3),InstantSnapshottable’ \
drl=on init=active
Note For information about using traditional DRL with an ISP volume, see “Adding Logs to a
Volume” on page 67. Such logs are implemented using a dedicated plex for each log copy,
rather than using a DCO volume, and are supported for mirrored volume layouts only.