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Chapter 4. LVM Administration Overview
This chapter provides an overview of the administrative procedures you use to configure LVM logical volumes. This chapter is intended to provide a general understanding of the steps involved. For specific step-by-step examples of common LVM configuration procedures, see Chapter 6, LVM Configuration Examples.
For descriptions of the CLI commands you can use to perform LVM administration, see Chapter 5, LVM Administration with CLI Commands. Alternately, you can use the LVM GUI, which is described in Chapter 8, LVM Administration with the LVM GUI.
4.1. Creating LVM Volumes in a Cluster
To create logical volumes in a cluster environment, you use the Clustered Logical Volume Manager (CLVM), which is a set of clustering extensions to LVM. These extensions allow a cluster of computers to manage shared storage (for example, on a SAN) using LVM. In order to use CLVM, the Red Hat Cluster Suite software, including the
clvmd daemon, must be started at boot time, as described in Section 2.4, “The Clustered Logical Volume Manager (CLVM)”.
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 GUI interface. 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.
CLVM requires changes to the
lvm.conf file for cluster-wide locking. Information on configuring the lvm.conf file to support clustered locking is provided within the lvm.conf file itself. For information about the lvm.conf file, see Appendix B, The LVM Configuration Files.
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 5.3.3, “Creating Volume Groups in a Cluster” and Section 5.3.8, “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. Asymmmetric cluster configurations in which some nodes have access to the storage and others do not are not supported.
Note
Shared storage for use in Red Hat Cluster Suite requires that you be running the cluster logical volume manager daemon (
clvmd) or the High Availability Logical Volume Management agents (HA-LVM). If you are not able to use either the clvmd daemon or HA-LVM for operational reasons or because you do not have the correct entitlements, you must not use single-instance LVM on the shared disk as this may result in data corruption. If you have any concerns please contact your Red Hat service representative.
For information on how to install Red Hat Cluster Suite and set up the cluster infrastructure, see Cluster Administration.
For an example of creating a mirrored logical volume in a cluster, see Section 6.5, “Creating a Mirrored LVM Logical Volume in a Cluster”.
