Managing HP Serviceguard for Linux, Sixth Edition, August 2006

Cluster and Package Maintenance
Single-Node Operation
Chapter 7 261
Single-Node Operation
The number of nodes you will need for your Serviceguard cluster depends
on the processing requirements of the applications you want to protect.
In a multi-node cluster, you could have a situation where all but one node
has failed, or where you have shut down all but one node, leaving your
cluster in single-node operation. This remaining node will probably have
applications running on it. As long as the Serviceguard daemon cmcld is
active, other nodes can re-join the cluster at a later time.
If the Serviceguard daemon fails when in single-node operation, it will
leave the single node up and your applications running. This is different
from the loss of the Serviceguard daemon in a multi-node cluster, which
halts the node with a TOC, and causes packages to be switched to
adoptive nodes. It is not necessary to halt the single node in this
scenario, since the application is still running, and no other node is
currently available for package switching.
You sh ould
not try to restart Serviceguard, since data corruption might
occur if another node were to attempt to start up a new instance of the
application that is still running on the single node.
Instead of restarting the cluster, choose an appropriate time to shutdown
and reboot the node, which will allow the applications to shut down and
then permit Serviceguard to restart the cluster after rebooting.