Creating a quorum disk

A quorum disk is used to resolve tie-break situations when the voting set of nodes disagree on the current state of the cluster.

Quorum disk creation and extent allocation

The use of a quorum disk allows the cluster to manage a SAN fault that splits the cluster exactly in half. One half of the cluster continues to operate and the other half stops until the SAN connectivity is restored.

During quorum disk discovery, the system assesses each logical unit (LU) to determine its potential use as a quorum disk. From the set of eligible LUs, the system nominates three quorum candidate disks.

An LU must meet the following criteria to be considered a candidate for a quorum disk:

It must be in managed space mode.
It must be visible to all nodes in the cluster.
It must be presented by a storage system that is an approved host for quorum disks.
It must have sufficient free extents to hold the cluster state and the configuration metadata.

If possible, the quorum disk candidates are presented by different devices. After the quorum candidate disks are selected, the cluster selects one of the candidate quorum disks to become the active quorum disk, which means it is used first to break a tie in the event of a cluster partition. After the active quorum disk is selected, the cluster does not attempt to ensure that the candidate quorum disks are presented by different devices. However, you can also manually select the active quorum disk if you want to ensure the active quorum disk is presented by a different device. Selecting the active quorum disk is useful in split-site cluster configurations and ensures that the most highly available quorum disk is used. You can set the -active parameter on the setquorum command to set a disk as an active quorum disk. You can also use the Set Active Quorum Disk panel in the SAN Volume Controller Console by selecting Work with Managed Disks > Quorum Disks to specify an active quorum disk. The quorum disk candidates can be updated by configuration activity if other eligible LUs are available.

To view a list of current quorum disk candidates, use the svcinfo lsquorum command.

If no quorum disk candidates are found after the discovery, one of the following situations has occurred:

No LUs exist in managed space mode. An error is logged when this situation occurs.
LUs exist in managed space mode, but they do not meet the eligibility criteria. An error is logged when this situation occurs.