Managing Serviceguard Eighteenth Edition, September 2010

The cluster lock disk is configured on an LVM volume group that is physically connected
to all cluster nodes. This volume group may also contain data that is used by packages.
When you are using dual cluster lock disks, it is required that the default I/O timeout
values are used for the cluster lock physical volumes. Changing the I/O timeout values
for the cluster lock physical volumes can prevent the nodes in the cluster from detecting
a failed lock disk within the allotted time period which can prevent cluster re-formations
from succeeding. To view the existing IO timeout value, run the following command:
pvdisplay <lock device file name>
The I/O Timeout value should be displayed as “default.” To set the IO Timeout back
to the default value, run the command:
pvchange -t 0 <lock device file name>
The use of a dual cluster lock is only allowed with certain specific configurations of
hardware. Refer to the discussion in Chapter 3 on “Dual Cluster Lock.” For instructions
on setting up a lock disk, see “Specifying a Lock Disk” (page 246).
Backing Up Cluster Lock Disk Information
After you configure the cluster and create the cluster lock volume group and physical
volume, you should create a backup of the volume group configuration data on each
lock volume group. Use the vgcfgbackup command for each lock volume group you
have configured, and save the backup file in case the lock configuration must be restored
to a new disk with the vgcfgrestore command following a disk failure.
NOTE: You must use the vgcfgbackup and vgcfgrestore commands to back up
and restore the lock volume group configuration data regardless of how you create the
lock volume group.
Setting Up a Lock LUN
LUN stands for Logical Unit Number. The term can refer to a single physical disk, but
these days is more often used in a SAN (Storage Area Network) or NAS
(Network-Attached Storage) context to denote a virtual entity derived from one or
more physical disks.
Keep the following points in mind when choosing a device for a lock LUN:
All the cluster nodes must be physically connected to the lock LUN.
A lock LUN must be a block device.
All existing data on the LUN will be destroyed when you configure it as a lock
LUN.
This means that if you use an existing lock disk, the existing lock information will
be lost, and if you use a LUN that was previously used as a lock LUN for a Linux
cluster, that lock information will also be lost.
226 Building an HA Cluster Configuration