A Red Hat Enterprise Linux High Availability Add-On cluster uses the
votequorum service, in conjunction with fencing, to avoid split brain situations. A number of votes is assigned to each system in the cluster, and cluster operations are allowed to proceed only when a majority of votes is present. The service must be loaded into all nodes or none; if it is loaded into a subset of cluster nodes, the results will be unpredictable. For information on the configuration and operation of the
votequorum service, see the
votequorum(5) man page.
10.1. Configuring Quorum Options
There are some special features of quorum configuration that you can set when you create a cluster with the
pcs cluster setup
command. Table 10.1, “Quorum Options”
summarizes these options.
Table 10.1. Quorum Options
When enabled, the cluster can suffer up to 50% of the nodes failing at the same time, in a deterministic fashion. The cluster partition, or the set of nodes that are still in contact with the
nodeid configured in
auto_tie_breaker_node (or lowest
nodeid if not set), will remain quorate. The other nodes will be inquorate.
option is principally used for clusters with an even number of nodes, as it allows the cluster to continue operation with an even split. For more complex failures, such as multiple, uneven splits, it is recommended that you use a quorum device, as described in Section 10.5, “Quorum Devices”
option is incompatible with quorum devices.
When enabled, the cluster will be quorate for the first time only after all nodes have been visible at least once at the same time.
wait_for_all option is primarily used for two-node clusters and for even-node clusters using the quorum device
lms (last man standing) algorithm.
wait_for_all option is automatically enabled when a cluster has two nodes, does not use a quorum device, and
auto_tie_breaker is disabled. You can override this by explicitly setting
wait_for_all to 0.
| When enabled, the cluster can dynamically recalculate |
expected_votes and quorum under specific circumstances. You must enable
wait_for_all when you enable this option. The
last_man_standing option is incompatible with quorum devices.
| The time, in milliseconds, to wait before recalculating |
expected_votes and quorum after a cluster loses nodes.
For further information about configuring and using these options, see the
votequorum(5) man page.