Installation guide

The Clustered Logical Volume Manager (CLVM)
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• If you are using a clustered system for failover where only a single node that accesses the storage
is active at any one time, you should use High Availability Logical Volume Management agents (HA-
LVM).
• If more than one node of your cluster will require access to your storage which is then shared
among the active nodes, then you must use CLVM. CLVM allows a user to configure logical volumes
on shared storage by locking access to physical storage while a logical volume is being configured,
and uses clustered locking services to manage the shared storage.
In order to use CLVM, the High Availability Add-On and Resilient Storage Add-On software, including
the clvmd daemon, must be running. The clvmd daemon is the key clustering extension to LVM.
The clvmd daemon runs in each cluster computer and distributes LVM metadata updates in a cluster,
presenting each cluster computer with the same view of the logical volumes. For information on
installing and administering the High Availability Add-On see Cluster Administration.
To ensure that clvmd is started at boot time, you can execute a chkconfig ... on command on
the clvmd service, as follows:
# chkconfig clvmd on
If the clvmd daemon has not been started, you can execute a service ... start command on
the clvmd service, as follows:
# service clvmd start
Creating LVM logical volumes in a cluster environment is identical to creating LVM logical volumes on
a single node. There is no difference in the LVM commands themselves, or in the LVM graphical user
interface, as described in Chapter 4, LVM Administration with CLI Commands and Chapter 7, LVM
Administration with the LVM GUI. In order to enable the LVM volumes you are creating in a cluster, the
cluster infrastructure must be running and the cluster must be quorate.
By default, logical volumes created with CLVM on shared storage are visible to all systems that have
access to the shared storage. It is possible to create volume groups in which all of the storage devices
are visible to only one node in the cluster. It is also possible to change the status of a volume group
from a local volume group to a clustered volume group. For information, see Section 4.3.2, “Creating
Volume Groups in a Cluster” and Section 4.3.7, “Changing the Parameters of a Volume Group”.
Warning
When you create volume groups with CLVM on shared storage, you must ensure that all nodes
in the cluster have access to the physical volumes that constitute the volume group. Asymmetric
cluster configurations in which some nodes have access to the storage and others do not are not
supported.
Figure 1.2, “CLVM Overview” shows a CLVM overview in a cluster.