Planning the Quorum Device (VxVM)

If you are using VERITAS Volume Manager (with or without the cluster feature), you must configure a quorum device regardless of the number of cluster nodes. During the Sun Cluster installation process, scinstall(1M) will prompt you to configure a quorum device.

The quorum device is either an array controller or a disk.

• If it is an array controller, all disks in the array must be part of the cluster applications. No private data (a private file system or disk groups private to a node) can be stored in the array controller.

• If the quorum device is a disk, that disk must be part of the cluster application. The disk cannot be private to either of the nodes.

During the cluster software installation, you will need to make decisions concerning:

• Type of quorum configuration (simple mode or complex mode) - In simple mode, the quorum device is configured automatically. In complex mode, you must configure the quorum device manually.

• Quorum device behavior - If the cluster is partitioned into subsets, you can configure the Cluster Membership Monitor either to automatically select which subset stays up, or to have the system prompt you for action.

• Quorum device policy - If you choose to have the system automatically select which subset stays up, you must configure the policy. You choose either lowest or highest node ID, to specify which subset of nodes automatically becomes the new cluster in the event the quorum device is activated. Refer to "Quorum, Quorum Devices, and Failure Fencing", for more information on the quorum device policy.

• Type of device - The quorum device can be a controller or disk in a multihost disk expansion unit.

  • If all the disks in an expansion unit are going to be used for shared disk groups (for OPS) or for HA disk groups, then the array controller can be used for the quorum device.

  • If one or more disks in an array are used for the private storage of a node (either as a file system or as a raw device), then one of the disks belonging either to the shared disk group (for OPS) or to one of the HA disk groups must be used as the quorum device.

  • You can also choose a dedicated disk as the quorum device (one on which no data is stored).

Cluster Topology Considerations

Before you select the quorum device for your cluster, be aware of the implications of your selection. Any node pair of the cluster must have a quorum device. That is, one quorum device must be specified for every node set that share multihost disks. Each node in the cluster must be informed of all quorum devices in the cluster, not just the quorum device connected to it. During cluster installation, the scinstall(1M) command displays all possible node pairs in sequence and displays any common devices that are quorum device candidates.

In two-node clusters with dual-ported disks, a single quorum device needs to specified.

In greater than two-node clusters with dual-ported disks, not all of the cluster nodes have access to the entire disk subsystem. In such configurations, you must specify one quorum device for each set of nodes that shares disks.

Sun Cluster configurations can consist of disk storage units (such as the Sun StorEdge A5000) that can be connected to all nodes in the cluster. This allows for applications such as OPS to run on clusters of greater than two nodes. A disk storage unit that is physically connected to all nodes in the cluster is referred to as a direct attached device. In this type of cluster a single quorum device needs to be selected from a direct attached device.

In clusters with direct attached devices, if the cluster interconnect fails, one of the following will happen:

• If manual intervention was specified when the quorum device was configured, all nodes will prompt for operator assistance.

• If automatic selection was specified when the quorum device was configured, the highest or lowest node ID will reserve the quorum device and all other nodes will prompt for operator assistance.

In clusters without direct attached devices to all nodes of the cluster, you will, by definition, have multiple quorum devices (one for each node pair that share disks). In this configuration, the quorum device only comes into play where only two nodes are remaining and they share a common quorum device.

In the event of a node failure, the node that is able to reserve the quorum device remains as the sole survivor of the cluster. This is necessary to ensure the integrity of data on the shared disks.