Managing Serviceguard Fifteenth Edition, reprinted May 2008

Understanding Serviceguard Software Components
How the Cluster Manager Works
Chapter 366
(described further in this chapter, in “How the Package Manager Works”
on page 74). 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 and initiate a
cluster re-formation that would not otherwise have been needed. For this
reason, HP recommends that you dedicate a LAN for the heartbeat as
well as configuring heartbeat over the data network.
NOTE You can no longer run the heartbeat on a serial (RS232) line or an FDDI
or Token Ring network.
IMPORTANT When multiple heartbeats are configured, heartbeats are sent in
parallel; Serviceguard must receive at least one heartbeat to establish
the health of a node. HP recommends that you configure all subnets that
connect cluster nodes as heartbeat networks; this increases protection
against multiple faults at no additional cost.
Heartbeat IP addresses are usually on the same subnet on each node, but
it is possible to configure a cluster that spans subnets; see “Cross-Subnet
Configurations” on page 41. See the entry for HEARTBEAT_IP, under
“Cluster Configuration Parameters” starting on page 156, for more
information about heartbeat requirements.
If you will be using the Veritas Cluster Volume Manager (CVM) Version
3.5 (on systems that support it) 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 on each node. See “Redundant
Heartbeat Subnet Required” on page 121.