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Sun Cluster 3.1 - 3.2 Hardware Administration Manual for Solaris OS

Determining the Number of Rooms in Your Cluster

The concept of a room, or location, adds a layer of complexity to the task of designing a campus cluster. Think of a room as a functionally independent hardware grouping, such as a node and its attendant storage, or a quorum device that is physically separated from any nodes. Each room is separated from other rooms to increase the likelihood of failover and redundancy in case of accident or failure. The definition of a room therefore depends on the type of failure to safeguard against, as described in the following table.

Table 7–1 Definitions of “Room”

Failure Scenario 

Sample Definitions of “Room” 

Power-line failure 

Isolated and independent power supplies 

Minor accidents, furniture collapse, water seepage 

Different parts of a physical room 

Small fire, fire sprinklers starting 

Different physical areas (for example, sprinkler zone) 

Structural failure, building-wide fire 

Different buildings 

Large-scale natural disaster (for example, earthquake or flood) 

Different corporate campuses up to several kilometers apart 

Sun Cluster does support two-room campus clusters. These clusters are valid and might offer nominal insurance against disasters. However, consider adding a small third room, possibly even a secure closet or vault (with a separate power supply and correct cabling), to contain the quorum device or a third server.

Whenever a two-room campus cluster loses a room, it has only a 50 percent chance of remaining available. If the room with fewest quorum votes is the surviving room, the surviving nodes cannot form a cluster. In this case, your cluster requires manual intervention from your Sun service provider before it can become available.

The advantage of a three-room or larger cluster is that, if any one of the three rooms is lost, automatic failover can be achieved. Only a correctly configured three-room or larger campus cluster can guarantee system availability if an entire room is lost (assuming no other failures).

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.

Note –

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

Illustration: A three-room, two-node campus cluster with the quorum device alone in the third room.

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

Illustration: A three-room, two-node campus cluster with minimum hardware requirements.

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

Illustration: A basic three-room, three-node campus cluster.

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:

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.