Managing Serviceguard 12th Edition, March 2006

Understanding Serviceguard Software Components
How the Cluster Manager Works
Chapter 3 65
cluster, that information is passed to the package coordinator
(described further in this chapter, in “How the Package Manager Works”
on page 73). Failover packages that were running on nodes that are no
longer in the new cluster are transferred to their adoptive nodes. Note
that if there is a transitory loss of heartbeat, the cluster may re-form
with the same nodes as before. In such cases, packages do not halt or
switch, though the application may experience a slight performance
impact during the re-formation.
If heartbeat and data are sent over the same LAN subnet, data
congestion may cause Serviceguard to miss heartbeats during the period
of the heartbeat timeout and initiate a cluster re-formation that would
not be needed if the congestion had not occurred. To prevent this
situation, it is recommended that you have a dedicated heartbeat as well
as configuring heartbeat over the data network or running heartbeat
over a serial (RS232) line. A dedicated LAN is not required, but you may
wish to use one if analysis of your networks shows a potential for loss of
heartbeats in the cluster.
NOTE You cannot run heartbeat on a serial line by itself. See “Using a Serial
(RS232) Heartbeat Line” on page 41 for more about serial lines in
Serviceguard.
IMPORTANT Multiple heartbeats are sent in parallel. It is normally recommended
that you configure all subnets that interconnect cluster nodes as
heartbeat networks, since this increases protection against multiple
faults at no additional cost. However, if you will be using the VERITAS
Cluster Volume Manager (CVM), Version 3.5, you can use only a single
heartbeat subnet. In this case, the heartbeat should be configured with
standby LANs or as a group of aggregated ports. See “Redundant
Heartbeat Subnet Required” on page 121
Each node sends its heartbeat message at a rate specified by the cluster
heartbeat interval. The cluster heartbeat interval is set in the cluster
configuration file, which you create as a part of cluster configuration,
described fully in Chapter 5, “Building an HA Cluster Configuration,” on
page 187