Setting quorum disks

You can set a managed disk (MDisk) as a quorum disk from the Setting a Quorum Disk panel.

This task assumes that you have already launched the SAN Volume Controller Console.

Quorum disks are used when there is a problem in the SAN fabric or when nodes are shut down, leaving half of the nodes remaining in the cluster. This type of problem causes a loss of communication between the nodes that remain in the cluster and those that do not. The nodes are split into groups where the nodes in each group can communicate with each other, but not with the other group of nodes that were formerly part of the cluster.

In this situation, some nodes must stop operating and processing I/O requests from hosts to preserve data integrity while maintaining data access. If a group contains less than half the nodes that were active in the cluster, the nodes in that group stop operating and processing I/O requests from hosts.

It is possible for a cluster to split into two groups with each group containing half the original number of nodes in the cluster. 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 marks their ownership of the quorum disk and as a result continues to operate as the cluster, handling all I/O requests. If the other group of nodes cannot access the quorum disk or finds it owned by another group of nodes, it stops operating as the cluster and does not handle I/O requests.

A quorum disk is formed by taking a small amount of space from a managed disk (MDisk). There is only one active quorum disk that is used to determine which nodes operate as the cluster. However, up to three candidate quorum disks are maintained. The purpose of the other quorum disks is to provide redundancy if a quorum disk fails prior to the cluster being split into two equal groups of nodes. The SAN Volume Controller automatically chooses up to three MDisk as quorum disk candidates and then automatically selects one of these as the active quorum disk. You can also manually set quorum disk candidates and the active quorum disk.

You must set quorum disks on multiple controllers to avoid the possibility of losing all of the quorum disks with a single failure. Mirrored virtual disks (VDisks) also are taken offline when all the quorum disks are on a single controller that experiences a failure. Mirrored VDisks are taken offline because synchronization data is stored on the quorum disks. To protect against mirrored VDisks being taken offline, follow these guidelines for changing the MDisk that are assigned as quorum disk candidates:

When possible, distribute the quorum candidate disks so that each MDisk is provided by a different storage system. For a list of storage systems that support quorum disks, refer to the Supported Hardware List located at the SAN Volume Controller (2145) Web site:
Support for SAN Volume Controller (2145)
Web site
Ensure that the status of the MDisk that is being set as a quorum disk is online before setting it as the quorum disk.
Wait at least two minutes between setting quorum disks. This delay allows time for the update to the quorum disk to complete before setting another quorum disk.

Attention: MDisks that are associated with solid-state drives (SSDs) on SAN Volume Controller 2145-CF8 nodes cannot be used as quorum disks.

Complete the following steps to set an MDisk as a quorum disk:

In the portfolio, click Work with Managed Disks > Quorum Disks. The Viewing Quorum Disks panel is displayed.
Select the MDisk to set as a quorum disk and select Set a Quorum Disk from the list. Click Go. The Setting a Quorum Disk panel is displayed.
Select a quorum index number from the Quorum Index list. and click OK.
If you want this disk to be used as the active quorum disk, select Set as Active Quorum Disk. The active quorum disk is the disk which is used first in the event of a cluster partition. You should set an active quorum disk when nodes in an I/O group are split between different physical locations to ensure that the most highly-available quorum disk is used.