Quorum disk
A quorum disk is an MDisk or a managed drive that contains a reserved area that is used exclusively for system management. A system automatically assigns quorum disk candidates. When you add new storage to a system or remove existing storage, however, it is a good practice to review the quorum disk assignments.
- To break a tie when a SAN fault occurs, when exactly half of the nodes that were previously a member of the system are present.
- To hold a copy of important system configuration data. Just over 256 MB is reserved for this purpose on each quorum disk candidate.
It is possible for a system to split into two groups where each group contains half the original number of nodes in the system. A quorum disk determines which group of nodes stops operating and processing I/O requests. In this tie-break situation, the first group of nodes that accesses the quorum disk is marked as the owner of the quorum disk and as a result continues to operate as the system, handling all I/O requests. If the other group of nodes cannot access the quorum disk or finds the quorum disk is owned by another group of nodes, it stops operating as the system and does not handle I/O requests.
A system can have only one active quorum disk that is used for a tie-break situation. However, the system uses three quorum disks to record a backup of system configuration data to be used in the event of a disaster. The system automatically selects one active quorum disk from these three disks. The active quorum disk can be specified by using the chquorum command-line interface (CLI) command with the active parameter. To view the current quorum disk status, use the lsquorum command. The other quorum disk candidates provide redundancy if the active quorum disk fails before a system is partitioned. To avoid the possibility of losing all the quorum disk candidates with a single failure, assign quorum disk candidates on multiple storage systems.