8.2. SCSI Fencing Requirements and Limitations

In order to configure your system to use SCSI persistent reservations to fence a node, you must be sure that the following conditions are met.

The sg3_utils package must be installed on your cluster nodes. This package provides the tools needed by the various scripts to manage SCSI persistent reservations.
All shared storage must use LVM2 cluster volumes.
All devices within the LVM2 cluster volumes must be SPC-3 compliant.

In addition to these requirements, fencing by way of SCSI persistent reservations is subject to the following limitations:

All nodes in the cluster must have a consistent view of storage. Each node in the cluster must be able to remove another node's registration key from all the devices that it registered with. In order to do this, the node performing the fencing operation must be aware of all devices that other nodes are registered with.
Devices used for the cluster volumes should be a complete LUN, not partitions. SCSI persistent reservations work on an entire LUN, meaning that access is controlled to each LUN, not individual partitions.
As of Red Hat Enterprise Linux 5.5 and fully-updated releases of Red Hat Enterprise Linux 5.4, SCSI fencing can be used in a 2-node cluster; previous releases did not support this feature.
As of Red Hat Enterprise Linux 5.5 and fully-updated releases of Red Hat Enterprise Linux 5.4, SCSI fencing can be used in conjunction with qdisk; previous releases did not support this feature. You cannot use fence_scsi on the LUN where qdiskd resides; it must be a raw LUN or raw partition of a LUN.