Arbitration For Data Integrity in Serviceguard Clusters, July 2007

Arbitration for Data Integrity in Serviceguard Clusters
Use of a Lock Disk as the Cluster Lock
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Use of a Lock Disk as the Cluster Lock
The cluster lock disk (used only in HP-UX clusters) is a disk that can be
written to by all members of the cluster. When a node obtains the cluster
lock, this disk is marked so that other nodes will recognize the lock as
“taken.” This mark will survive an off-on power cycle of the disk device
unlike SCSI disk reservations. A lock disk may be used for clusters of up
to four nodes.
The lock is created in a special area on a particular LVM physical
volume. The cluster lock volume group and physical volume names are
identified in the cluster configuration file.
The lock disk is not dedicated for use as the cluster lock; thus, it can be
employed as part of a normal volume group with user data on it. The
usable space on the disk is not impacted; the lock disk takes no space
away from the disk’s volume group. Further, the activation of the volume
group on one node does not affect the ability of another node to acquire
the cluster lock.
The lock area on the disk is not mirrored, even though the physical
volume may be a part of a volume group that contains mirrored logical
volumes.
The operation of the lock disk is shown in Figure 5. The node that
acquires the lock (in this case node 2) continues running in the cluster.
The other node halts.
Figure 5 Lock Disk Operation