Managing Serviceguard 11th Edition, Version A.11.16, Second Printing June 2004

Understanding Serviceguard Software Components
How the Cluster Manager Works
Chapter 3 63
Packages which 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. Refer to Chapter 2,
“Using a Serial (RS232) Heartbeat Line,” for details 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), 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 below, “Single Heartbeat
Subnet Required with CVM.”
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 the chapter “Building an HA Cluster Configuration.”