Managing Serviceguard Fifteenth Edition, reprinted May 2008

Understanding Serviceguard Hardware Configurations
Larger Clusters
Chapter 254
Larger Clusters
You can create clusters of up to 16 nodes with Serviceguard. Clusters of
up to 16 nodes may be built by connecting individual SPUs via Ethernet.
The possibility of configuring a cluster consisting of 16 nodes does not
mean that all types of cluster configuration behave in the same way in a
16-node configuration. For example, in the case of shared SCSI buses, the
practical limit on the number of nodes that can be attached to the same
shared bus is four, because of bus loading and limits on cable length.
Even in this case, 16 nodes could be set up as an administrative unit, and
sub-groupings of four could be set up on different SCSI buses which are
attached to different mass storage devices.
In the case of non-shared SCSI connections to an XP series or EMC disk
array, the four-node limit does not apply. Each node can be connected
directly to the XP or EMC by means of two SCSI buses. Packages can be
configured to fail over among all sixteen nodes. For more about this type
of configuration, see “Point to Point Connections to Storage Devices,”
below.
NOTE When configuring larger clusters, be aware that cluster and package
configuration times as well as execution times for commands such as
cmviewcl will be extended. In the man pages for some commands, you
can find options to help to reduce the time. For example, refer to the man
page for cmquerycl for options that can reduce the amount of time
needed for probing disks or networks.
Active/Standby Model
You can also create clusters in which there is a standby node. For
example, an eight node configuration in which one node acts as the
standby for the other seven could easily be set up by equipping the
backup node with seven shared buses allowing separate connections to
each of the active nodes. This configuration is shown in Figure 2-5.