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Managing HP Serviceguard for Linux, Eighth Edition, March 2008

ManualsBrandsHP ManualsSoftwareHP SAP Linux Serviceguard Cluster Extension
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Understanding Serviceguard Software Components
How the Cluster Manager Works
Chapter 3 45
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.
Automatic Cluster Startup
An automatic cluster startup occurs any time a node reboots and joins
the cluster. This can follow the reboot of an individual node, or it may be
when all nodes in a cluster have failed, as when there has been an
extended power failure and all SPUs went down.
Automatic cluster startup will take place if the flag AUTOSTART_CMCLD is
set to 1 in the $SGCONF/cmcluster.rc file. When any node reboots with
this parameter set to 1, it will rejoin an existing cluster, or if none exists
it will attempt to form a new cluster.
Dynamic Cluster Re-formation
A dynamic re-formation is a temporary change in cluster membership
that takes place as nodes join or leave a running cluster. Re-formation
differs from reconfiguration, which is a permanent modification of the
configuration files. Re-formation of the cluster occurs under the following
conditions (not a complete list):
• An SPU or network failure was detected on an active node.
• An inactive node wants to join the cluster. The cluster manager
daemon has been started on that node.
• A node has been added to or deleted from the cluster configuration.
• The system administrator halted a node.
• A node halts because of a package failure.
• A node halts because of a service failure.
• Heavy network traffic prohibited the heartbeat signal from being
received by the cluster.
• The heartbeat network failed, and another network is not configured
to carry heartbeat.
Typically, re-formation results in a cluster with a different composition.
The new cluster may contain fewer or more nodes than in the previous
incarnation of the cluster.