HP StorageWorks XP Cluster Extension Software Administrator Guide (T1656-96035, April 2010)

or remote site, the other site together with the added node would have a majority. In a MNS with
File Share Witness configuration, the, file share should be located at the third site.
TIP:
To upgrade XP firmware while the application service is running, use host load balancing and
multipathing software, such as Auto Path, HP MPIO Full Featured Device Specific Module (DSM) for
XP family of Disk Arrays (HP MPIO XP DSM), or VERITAS for Sun Solaris.
XP Cluster Extension allows you to configure the failover behavior so that the application service
startup is stopped if no remote cluster members can be reached. The default configuration of XP Cluster
Extension expects the cluster software to deal with the split-brain syndrome.
Planning for XP Cluster Extension
Before configuring XP Cluster Extension resources
Before configuring XP Cluster Extension resources for the Windows CLI implementation or Unix
environments, review the XP Cluster Extension objects in the UCF.cfg file. For more information about
XP Cluster Extension objects, see Chapter 8 on page 123.
Cluster setup considerations
For cluster setup considerations that apply to Windows and Linux, see:
• MNS quorum clusters (MSCS), page 15
• SLE HA cluster setup considerations, page 15
• RHCS cluster setup considerations, page 18
MNS quorum clusters (MSCS)
In an MNS cluster, the cluster service is allowed to start or run only if it has access to the majority of
the configured nodes.
This means that losing half the nodes in a 2-, 4-, 6-, or 8-node cluster or losing the communication
links with 50% of the nodes on each site forces every node to terminate the cluster services because
none of them have access to a majority of the configured nodes.
Therefore, a geographically dispersed MNS-based cluster requires an additional node per cluster
located at a third site so that whenever a disaster affects either the local or remote site, the other site
together with the added node has a majority.
SLE HA cluster setup considerations
Follow the guidelines in this section when you configure clusters for use with XP Cluster Extension.
Quorum
In an SLE HA cluster, quorum is defined as a strict majority of the defined cluster (more than 50%).
With certain failures, a cluster might be divided into two subclusters. In an SLE HA cluster, a subcluster
with more than 50% of the nodes wins the quorum. The subcluster that wins the quorum re-forms the
cluster and fences the subcluster that lost the quorum. The behavior of the subcluster that lost the
XP Cluster Extension Software Administrator Guide 15