Three-Room Campus Cluster Examples

A three-room campus cluster configuration supports up to eight nodes. Three rooms enable you to arrange your nodes and quorum device so that your campus cluster can reliably survive the loss of a single room and still provide cluster services. Mediators are also supported for three-room campus clusters that use Solaris Volume Manager or multi-owner Solaris Volume Manager. The following example configurations all follow the campus cluster requirements and the design guidelines described in this chapter.

• Figure 7–1 shows a three-room, two-node campus cluster. In this arrangement, two rooms each contain a single node and an equal number of disk arrays to mirror shared data. The third room contains at least one disk subsystem, attached to both nodes and configured with a quorum device.

• Figure 7–2 shows an alternative three-room, two-node campus cluster.

• Figure 7–3 shows a three-room, three-node cluster. In this arrangement, two rooms each contain one node and an equal number of disk arrays. The third room contains a small server, which eliminates the need for a storage array to be configured as a quorum device.

• Mediators for three-room campus clusters that use Solaris Volume Manager or multi-owner Solaris Volume Manager are supported. The third mediator host exists outside the campus cluster and does not need to be attached to the shared storage. See Solaris Volume Manager Three-Mediator Support for more information.

These examples illustrate general configurations and are not intended to indicate required or recommended setups. For simplicity, the diagrams and explanations concentrate only on features that are unique to understanding campus clustering. For example, public-network Ethernet connections are not shown.

Figure 7–1 Basic Three-Room, Two-Node Campus Cluster Configuration With Multipathing

In the configuration that is shown in the following figure, if at least two rooms are up and communicating, recovery is automatic. Only three-room or larger configurations can guarantee that the loss of any one room can be handled automatically.

Figure 7–2 Minimum Three-Room, Two-Node Campus Cluster Configuration Without Multipathing

In the configuration shown in the following figure, one room contains one node and shared storage. A second room contains a cluster node only. The third room contains shared storage only. A LUN or disk of the storage device in the third room is configured as a quorum device.

This configuration provides the reliability of a three-room cluster with minimum hardware requirements. This campus cluster can survive the loss of any single room without requiring manual intervention.

Figure 7–3 Three-Room, Three-Node Campus Cluster Configuration

In the configuration that is shown in the preceding figure, a server acts as the quorum vote in the third room. This server does not necessarily support data services. Instead, it replaces a storage device as the quorum device.

Solaris Volume Manager Three-Mediator Support

Sun Cluster software supports mediators for three-room campus cluster configurations that use Solaris Volume Manager or multi-owner Solaris Volume Manager for Sun Cluster. A two-room (two-node) campus cluster can work with a third mediator host outside the cluster. The third mediator host does not have to be attached to the shared storage that contains the disk set for which the host is a mediator.

The mediator host uses Solaris Volume Manager to facilitate automatic recovery for a two-room campus cluster by tracking which mirrored half of the storage is the most up to date. The third mediator then provides mediator quorum to allow Solaris Volume Manager to recover from a destroyed room.

Use the following guidelines to configure dual-string mediators:

• A disk set can have up to three mediator hosts

• The mediator host no longer needs to be part of the cluster

• Mediators that are configured for disk sets must meet the existing two-string disk set criteria

• The entire campus cluster can have more than two nodes

• An N+1 cluster and other topologies are permitted

To add the third mediator host, follow the instructions in How to Add Mediator Hosts in Sun Cluster Software Installation Guide for Solaris OS. See the appropriate documentation for Sun Cluster 3.1 or Sun Cluster 3.2 software.