Managing HP Serviceguard for Linux, Seventh Edition, July 2007

Planning and Documenting an HA Cluster
Cluster Configuration Planning
Chapter 4 111
• To ensure the fastest cluster reformations, use the
default value. But keep in mind that this setting
can lead to reformations that are caused by
short-lived system hangs or network load spikes.
• For fewer reformations, use a setting in the range
of 5,000,000 to 8,000,000 microseconds (5 to 8
seconds). But keep in mind that this will lead to
slower reformations than the default value.
• The maximum recommended value is 30,000,000
microseconds (30 seconds).
Remember that a cluster reformation may result in a
system reboot on one of the cluster nodes.
There are more complex cases that require you to make
a trade-off between fewer failovers and faster failovers.
For example, a network event such as a broadcast
storm may cause kernel interrupts to be turned off on
some or all nodes while the packets are being
processed, preventing the nodes from sending and
processing heartbeat messages. This in turn could
prevent the kernel’s safety timer from being reset,
causing the node to halt. (See “Cluster Daemon: cmcld”
on page 35 for more information about the safety
timer.)
Can be changed while the cluster is running.
AUTO_START_TIMEOUT
The amount of time a node waits before it stops trying
to join a cluster during automatic cluster startup. All
nodes wait this amount of time for other nodes to begin
startup before the cluster completes the operation. The
time should be selected based on the slowest boot time
in the cluster. Enter a value equal to the boot time of
the slowest booting node minus the boot time of the
fastest booting node plus 600 seconds (ten minutes).
Default is 600,000,000 microseconds.
Can be changed while the cluster is running.