Managing HP Serviceguard for Linux, Eighth Edition, March 2008

Understanding Serviceguard Software Components
How the Cluster Manager Works
Chapter 344
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.
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
interconnect cluster nodes as heartbeat networks; this increases
protection against multiple faults at no additional cost.
Heartbeat IP addresses must be on the same subnet on each node, but it
is possible to configure a cluster that spans subnets; see “Cross-Subnet
Configurations” on page 30. See the entry for HEARTBEAT_IP, under
“Cluster Configuration Parameters” starting on page 110, for more
information about heartbeat requirements.
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 in Chapter 5, “Building an HA Cluster Configuration,” on
page 141.
Manual Startup of Entire Cluster
A manual startup forms a cluster out of all the nodes in the cluster
configuration. Manual startup is normally done the first time you bring
up the cluster, after cluster-wide maintenance or upgrade, or after
reconfiguration.
Before startup, the same binary cluster configuration file must exist on
all nodes in the cluster. The system administrator starts the cluster with
the cmruncl command issued from one node. The cmruncl command can
only be used when the cluster is not running, that is, when none of the
nodes is running the cmcld daemon.