Installation guide

Please note, that the SCSI fencing mechanism requires persistent SCSI reservations. Please

contact Red Hat technical support and your storage hardware vendor if your software and

hardware configuration supports persistent SCSI reservations.

4.8 CLVM

Consistency must be ensured in all cluster configurations. Logical volume configurations are

protected by the use of CLVM. CLVM is an extension to standard Logical Volume

Management (LVM) that distributes LVM metadata updates to the cluster. The CLVM daemon

(clvmd) must be running on all nodes in the cluster and will produce an error if any node in the

cluster does not have this daemon running.

4.9 Storage Mirroring

In disaster tolerant configurations, storage mirroring techniques are used to protect data and

ensure availability in the event of a storage array loss. Storage mirroring is normally

performed in two different ways.

Enterprise storage arrays typically offer the mechanism to mirror all data from one storage

array to one or more other arrays. In the case of a disaster, remote data copies can be used.

In Red Hat Enterprise Linux 5.3, Red Hat offers the possibility to create cluster aware host

based mirroring configurations. With the cmirror device mapper plugin, all servers in the

cluster are able to create mirrors of independent storage arrays in order to prevent data loss

and ensure availability in case of disaster.

CLVM is used to manage and monitor the mirrored logical volumes.