Managing Serviceguard 13th Edition, February 2007

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 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, 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.
IMPORTANT When multiple heartbeats are configured, heartbeats are sent in
parallel. HP recommends that you configure all subnets that
interconnect cluster nodes as heartbeat networks; 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 (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. See “Redundant Heartbeat Subnet Required”
on page 124.
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.