HP Serviceguard A.11.20- Managing Serviceguard Twentieth Edition, August 2011

2 Understanding Serviceguard Hardware Configurations
This chapter gives a broad overview of how the Serviceguard hardware components work. The
following topics are presented:
• Redundancy of Cluster Components
• Redundant Network Components (page 28)
• Redundant Disk Storage (page 32)
• Redundant Power Supplies (page 37)
• Larger Clusters (page 37)
Refer to the next chapter for information about Serviceguard software components.
Redundancy of Cluster Components
In order to provide a high level of availability, a typical cluster uses redundant system components,
for example two or more SPUs and two or more independent disks. This redundancy eliminates
single points of failure. In general, the more redundancy, the greater your access to applications,
data, and supportive services in the event of a failure.
In addition to hardware redundancy, you must have the software support which enables and
controls the transfer of your applications to another SPU or network after a failure. Serviceguard
provides this support as follows:
• In the case of LAN failure, Serviceguard switches to a standby LAN or moves affected packages
to a standby node.
• In the case of SPU failure, your application is transferred from a failed SPU to a functioning
SPU automatically and in a minimal amount of time.
• For failure of other monitored resources, such as disk interfaces, a package can be moved to
another node.
• For software failures, an application can be restarted on the same node or another node with
minimum disruption.
Serviceguard also gives you the advantage of easily transferring control of your application to
another SPU in order to bring the original SPU down for system administration, maintenance, or
version upgrades.
The current maximum number of nodes supported in a Serviceguard cluster is 16. SCSI disks or
disk arrays can be connected to a maximum of 4 nodes at a time on a shared (multi-initiator) bus.
Disk arrays using fibre channel and those that do not use a shared bus — such as the HP
StorageWorks XP Series and the EMC Symmetrix — can be simultaneously connected to all 16
nodes.
The guidelines for package failover depend on the type of disk technology in the cluster. For
example, a package that accesses data on a SCSI disk or disk array can failover to a maximum
of 4 nodes. A package that accesses data from a disk in a cluster using Fibre Channel or HP
StorageWorks XP or EMC Symmetrix disk technology can be configured for failover among 16
nodes.
Note that a package that does not access data from a disk on a shared bus can be configured to
fail over to as many nodes as you have configured in the cluster (regardless of disk technology).
For instance, if a package only runs local executables, it can be configured to failover to all nodes
in the cluster that have local copies of those executables, regardless of the type of disk connectivity.
Redundancy of Cluster Components 27