A quorum server can be used in clusters of any size. The quorum
server is an alternate form of cluster lock that uses a server program
running on a separate system for tie-breaking rather than a lock
disk. Should two equal sized groups of nodes (exactly 50% of the
cluster in each group) become separated from each other, the quorum
server allows one group to achieve quorum and form the cluster,
while the other group is denied quorum and cannot start a cluster.
The quorum server process runs on a machine outside
of the cluster for which it is providing quorum services.
The quorum server listens to connection requests from the Serviceguard nodes
on a known port. The server maintains a special area in memory for
each cluster, and when a node obtains the cluster lock, this area
is marked so that other nodes will recognize the lock as “taken.” The
cluster will maintain this mark during an off-on power cycle of
the quorum server.
The operation of the quorum server is shown in Figure 7.
When there is a loss of communication between node 1 and node 2,
the quorum server chooses one node (in this example, node 2) to
continue running in the cluster. The other node halts.
The quorum server runs on a Linux or HP-UX system.You can configure the
quorum server as a Serviceguard package in another cluster; it must be
a cluster other than the one for which it is providing quorum services. A
quorum server, whether or not it is running as a package, can provide quorum
services for multiple clusters.
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 | NOTE: Consult your Configuration
Guide for up-to-the-minute information on types of supported
quorum server configuration, as well as on support of quorum server
as a package. |
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Setting
up the Quorum Server |
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If you are using a quorum server (QS), the QS software, which
has to be running during cluster configuration, must be installed
on a system other than the nodes on which your cluster will be running.
This can be either a single HP-UX or Linux system.
Running
the Quorum Server
The quorum server must be running during the following cluster operations:
when the cmquerycl command is issued.
when the cmapplyconf command is issued.
when there is a cluster re-formation.
Specifying
a Quorum Server
If you will be using a quorum server, be sure to specify the -q qshost option with the cmquerycl command. Example:
# cmquerycl -v -n lp1 -n lp2 -q lp-qs -C clus-lp.config
Quorum
Server Status and State
The status of the
quorum server can be one of the following:
Up. The quorum server
is active.
Down. The quorum server is not
active.
The state of the
quorum server can be one of the following:
Running. Quorum services
are active and available.
Unsupported Version. There is a
version mismatch between Serviceguard and Quorum Server.
Access Denied. The Serviceguard
node is not authorized to access the quorum server system.
Unknown. Serviceguard cannot determine
whether the quorum server is up or down. This may happen when the
quorum server cannot be reached from the current node.
Viewing
Quorum Server Status and State
If the cluster is using a quorum server for tie-breaking services,
you can use the cmviewcl command to display the server name, state, and status following
the entry for each node, as in the following excerpt from the output
of cmviewcl -v:
CLUSTER STATUS
clus-lp up
NODE STATUS STATE
lp1 up running
Quorum Server Status:
NAME STATUS STATE
lp-qs up running
...
NODE STATUS STATE
lp2 up running
Quorum Server Status:
NAME STATUS STATE
lp-qs up running |
Viewing
Quorum Server System Data
You can also log on to the quorum server system itself and
use the ps command to confirm that the qs process is running. In
addition, you can view data about connections from cluster nodes
in the quorum server log file.
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