2. Clustering Updates

Clusters are multiple computers (nodes) working in concert to increase reliability, scalability, and availability to critical production services.
All updates to clustering in Red Hat Enterprise Linux 5.4 are detailed in the Technical Notes. Further information on clustering in Red Hat Enterprise Linux is available in the Cluster Suite Overview and the Cluster Administration documents.
Cluster Suite tools have been upgraded to support automatic hypervisor detection. However, running the cluster suite in conjunction with KVM hypervisor is considered to be a Technology Preview.
OpenAIS now provides broadcast network communication in addition to multicast. This functionality is considered Technology Preview for standalone usage of OpenAIS and for usage with the Cluster Suite. Note, however, that the functionality for configuring OpenAIS to use broadcast is not integrated into the cluster management tools and must be configured manually.

Note

SELinux in Enforcing mode is not supported with the Cluster Suite; Permissive or Disabled modes must be used. Using Cluster Suite on bare metal PPC systems is not supported. Guests running Cluster Suite on VMWare ESX hosts and using fence_vmware is considered a Technology Preview. Running Cluster Suite in guests on VMWare ESX hosts that are managed by Virtual Center is not supported.
Mixed architecture clusters using Cluster Suite are not supported. All Nodes in the cluster must be of the same architecture. For the purposes of Cluster Suite, x86_64, x86 and ia64 are considered to be the same architecture, so running clusters with combinations of these architectures is supported.

2.1. Fencing Improvements

Fencing is the disconnection of a node from the cluster's shared storage. Fencing cuts off I/O from shared storage, thus ensuring data integrity.
In Red Hat Enterprise Linux 5.4, fencing support on Power Systems has been added, as a Technology Preview, for IBM Logical Partition (LPAR) instances that are managed using the Hardware Management Console (HMC) (BZ#485700). Fencing support has also been added, as a Technology Preview for Cisco MDS 9124 & Cisco MDS 9134 Multilayer Fabric Switches (BZ#480836).
The fence_virsh fence agent is provided in this release of Red Hat Enterprise Linux as a Technology Preview. fence_virsh provides the ability for one guest (running as a domU) to fence another using the libvirt protocol. However, as fence_virsh is not integrated with cluster-suite it is not supported as a fence agent in that environment.
The fence_scsi man page has been updated, detailing the following limitations:
The fence_scsi fencing agent requires a minimum of three nodes in the cluster to operate.  For an FC connected SAN devices, these must be physical nodes.  SAN devices connected via iSCSI may use virtual or physical nodes.  In addition, fence_scsi cannot be used in conjunction with qdisk.
Additionally, the following new articles on fencing have been published on the Red Hat Knowledge Base: