Managing HP Serviceguard for Linux, Sixth Edition, August 2006

Understanding Serviceguard Software Components
How the Cluster Manager Works
Chapter 3 39
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. 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.
Multiple heartbeats are sent in parallel. It is recommended that you
configure all subnets that interconnect cluster nodes as heartbeat
networks, since this increases protection against multiple faults at no
additional cost. Heartbeat networks are specified with the HEARTBEAT_IP
cluster configuration parameter.
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.”
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.
During startup, the cluster manager software checks to see if all nodes
specified in the startup command are valid members of the cluster, are
up and running, are attempting to form a cluster, and can communicate
with each other. If they can, then the cluster manager forms the cluster.