Use of a Lock LUN as the Cluster Lock

The lock LUN is similar to the HP-UX cluster lock disk but different in certain respects. As with the lock disk, a lock LUN is marked when a node obtains the cluster lock, so that other nodes will see the lock as “taken.” This mark will survive an off-on power cycle of the disk device unlike SCSI disk reservations. As with HP-UX, the lock LUN can be used with clusters of up to four nodes. The lock LUN is not mirrored.

Here are the important differences between the lock disk in HP-UX and the lock LUN in Linux or HP-UX:

Only a single lock LUN can be configured. Dual cluster locking with lock LUN is not supported. Therefore for extended-distance disaster tolerant configurations a Quorum Server is required.
The lock LUN is created on a Linux partition, or HP-UX partition or disk, directly, not through LVM. The lock LUN is not part of a volume group.
The lock LUN partition is dedicated for cluster lock use; however, in Linux clusters, and HP-UX Integrity clusters, other partitions on the same storage unit can be used for shared storage. A lock LUN requires about 100 KB.
In clusters consisting of HP-UX Integrity servers only, you can use the idisk (1m) utility to create a partition for the lock LUN. In clusters that include HP 9000 servers, you must use an entire disk or LUN. On Linux systems, use the fdisk command to define the partition as type Linux (83).

Serviceguard periodically checks the health of the lock LUN and writes messages to the syslog file when a lock LUN fails the health check. This file should be monitored for early detection of lock disk problems.

The operation of the lock LUN is shown in Figure 1-6 “Lock LUN Operation”. The node that acquires the lock (in this case node 2) continues running in the cluster. The other node halts.

Figure 1-6 Lock LUN Operation

Use of a Lock LUN as the Cluster Lock

Technical documentation

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