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.|
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 “Eight-Node
Active/Standby Cluster ”.
Figure 2-5 Eight-Node
to Point Connections to Storage Devices
Some storage devices allow point-to-point connection to a
large number of host nodes without using a shared SCSI bus. An example
is shown in Figure 2-11, a cluster consisting of eight nodes with
a SCSI interconnect. The nodes access shared data on an XP or EMC
disk array configured with 16 SCSI I/O ports. Each node is connected
to the array using two separate SCSI channels. Each channel is a
dedicated bus; there is no daisy-chaining of the SCSI bus.
Figure 2-6 Eight-Node
Cluster with XP or EMC Disk Array
Fibre Channel switched configurations also are supported using
either an arbitrated loop or fabric login topology. For additional
information about supported cluster configurations, refer to the HP
Unix Servers Configuration Guide, available through
your HP representative.