Managing HP Serviceguard for Linux, Seventh Edition, July 2007

Understanding Serviceguard Software Components
Responses to Failures
Chapter 3 85
1. The node tries to reform the cluster.
2. If the node cannot get a quorum (if it cannot get the cluster lock) then
3. The node halts (system reset).
Example
Situation. Assume a two-node cluster, with Package1 running on
SystemA and Package2 running on SystemB. Volume group vg01 is
exclusively activated on SystemA; volume group vg02 is exclusively
activated on SystemB. Package IP addresses are assigned to SystemA
and SystemB respectively.
Failure. Only one LAN has been configured for both heartbeat and data
traffic. During the course of operations, heavy application traffic
monopolizes the bandwidth of the network, preventing heartbeat packets
from getting through.
Since SystemA does not receive heartbeat messages from SystemB,
SystemA attempts to reform as a one-node cluster. Likewise, since
SystemB does not receive heartbeat messages from SystemA, SystemB
also attempts to reform as a one-node cluster. During the election
protocol, each node votes for itself, giving both nodes 50 percent of the
vote. Because both nodes have 50 percent of the vote, both nodes now vie
for the cluster lock. Only one node will get the lock.
Outcome. Assume SystemA gets the cluster lock. SystemA reforms as a
one-node cluster. After reformation, SystemA will make sure all
applications configured to run on an existing clustered node are running.
When SystemA discovers Package2 is not running in the cluster it will
try to start Package2 if Package2 is configured to run on SystemA.
SystemB recognizes that it has failed to get the cluster lock and so
cannot reform the cluster. To release all resources related to Package2
(such as exclusive access to volume group vg02 and the Package2 IP
address) as quickly as possible, SystemB halts (system reset).
NOTE If AUTOSTART_CMCLD in /etc/rc.config.d/cmcluster ($SGAUTOSTART)
is set to zero, the node will not attempt to join the cluster when it comes
back up.