Managing Serviceguard 14th Edition, June 2007

Understanding Serviceguard Software Components

Serviceguard Architecture

Chapter 3 59

For services, cmcld monitors the service process and, depending on the

number of service retries, cmcld either restarts the service through

cmsrvassistd or it causes the package to halt and moves the package to

an available alternate node.

Quorum Server Daemon: qs

Using a quorum server is one way to break a tie and establish a

quorum when the cluster is re-forming; the other way is to use a cluster

lock. See “Cluster Quorum to Prevent Split-Brain Syndrome” and

“Cluster Lock” on page 65.

The quorum server, if used, runs on a system external to the cluster and

is started by the system administrator, not by Serviceguard. It is

normally started from /etc/inittab with the respawn option, which

means that it automatically restarts if it fails or is killed. All members of

the cluster initiate and maintain a connection to the quorum server; if it

dies, the Serviceguard nodes will detect this and then periodically try to

reconnect to it. If there is a cluster re-formation while the quorum server

is down and tie-breaking is needed, the re-formation will fail and all the

nodes will halt (system reset). For this reason it is important to bring the

quorum server back up as soon as possible.

Network Manager Daemon: cmnetd

This daemon monitors the health of cluster networks, and performs local

LAN failover. It also handles the addition and deletion of relocatable

package IP(s), for both IPv4 and IPv6 addresses.

Lock LUN Daemon: cmldisklockd

If a lock LUN is being used, cmdisklockd runs on each node in the

cluster and is started by cmcld when the node joins the cluster.

Each member of the cluster initiates and maintains a connection to the

cmdisklockd daemon locally. If the cmdisklockd daemon dies it will be

restarted by cmcld and the node will reconnect to it. If there is a cluster

reconfiguration while cmdisklockd is down and there is a partition in

the cluster that requires tie-breaking, the reconfiguration will fail.