Veritas Volume Manager 4.1 Administrator's Guide (HP-UX 11i v3, February 2007)

Chapter 13, Administering Cluster Functionality
Dirty Region Logging (DRL) in Cluster Environments
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Once you have installed the new release on all nodes, run the vxdctl upgrade
command on the master node to switch the cluster to the higher cluster protocol version.
See “Upgrading the Cluster Protocol Version” on page 379 for more information.
Dirty Region Logging (DRL) in Cluster Environments
Dirty region logging (DRL) is an optional property of a volume that provides speedy
recovery of mirrored volumes after a system failure. DRL is supported in cluster-shareable
disk groups. This section provides a brief overview of how DRL behaves in a cluster
environment. For more information on DRL, see “Dirty Region Logging (DRL)” on
page 42.
In a cluster environment, the VxVM implementation of DRL differs slightly from the
normal implementation.
A dirty region log on a system without cluster support has a recovery map and a single
active map. A dirty region log in a cluster, however, has one recovery map and one active
map for each node in the cluster.
The dirty region log size in clusters is typically larger than in non-clustered systems, as it
must accommodate a recovery map plus active maps for each node in the cluster. The size
of each map within the dirty region log is one or more whole blocks. The vxassist
command automatically allocates a sufficiently large dirty region log for the size of the
volume and the number of nodes.
It is possible to reimport a non-shared disk group (and its volumes) as a shared disk group
in a cluster environment. However, the dirty region logs of the imported disk group may
be considered invalid and a full recovery may result.
If a shared disk group is imported as a private disk group on a system without cluster
support, VxVM considers the logs of the shared volumes to be invalid and conducts a full
volume recovery. After the recovery completes, VxVM uses DRL.
The cluster functionality of VxVM can perform a DRL recovery on a non-shared volume.
However, if such a volume is moved to a VxVM system with cluster support and
imported as shared, the dirty region log is probably too small to accommodate maps for
all the cluster nodes. VxVM then marks the log invalid and performs a full recovery
anyway. Similarly, moving a DRL volume from a two-node cluster to a four-node cluster
can result in too small a log size, which the cluster functionality of VxVM handles with a
full volume recovery. In both cases, you must allocate a new log of sufficient size.