1.2.2 Cluster Interconnect

The cluster interconnect provides a reliable internode communication channel used for vital locking and heartbeat information. The interconnect is used for maintaining cluster availability, synchronization, and integrity. The cluster interconnect is composed of two private links. These links are redundant; only one is required for cluster operation. If all nodes are up and a single private interconnect is lost, cluster operation will continue. However, when a node joins the cluster, both private interconnects must be operational for the join to complete successfully.

By convention throughout this guide the network adapter interfaces hme1 and hme2 are shown as the cluster interconnect. Your interface names can vary depending on your hardware platform and your private network configuration. The requirement is that the two private interconnects do not share the same controller and thus cannot be disrupted by a single point of failure.

Clusters can use either the Scalable Coherent Interface (SCI) or Fast Ethernet as the private interconnect medium. However, support for mixed configurations (that is, both SCI and Ethernet private interconnects in the same cluster) is not supported.

1.2.2.1 The Switch Management Agent

The Switch Management Agent (SMA) is a cluster module that maintains communication channels over the private interconnect. It monitors the private interconnect and performs a failover of the logical adapter on the surviving private network if it detects a failure. In the case of more than one failure, SMA notifies the Cluster Membership Monitor which will take any action needed to change the cluster membership.

Clustered environments have different communication needs depending on the types of data services they support. Clusters providing only HA data services need only the heartbeat and minimal cluster configuration traffic over the private interconnect, and for these configurations Fast Ethernet is more than adequate. Clusters providing parallel database services send substantial amounts of traffic over the private interconnect. These applications benefit from the increased throughput of SCI.

SMA for SCI Clusters

The Scalable Coherent Interface (SCI) is a memory-based high-speed interconnect that enables sharing of memory among cluster nodes. The SCI private interconnect consists of Transmission Control Protocol/Internet Protocol (TCP/IP) network interfaces based on SCI.

Clusters of all sizes may be connected through a switch or hub. However, only two-node clusters may be connected point-to-point. The Switch Management Agent (SMA) software component manages sessions for the SCI links and switches.

There are three basic SCI topologies supported in Sun Cluster (Figure 1-1 and Figure 1-2):

• Three- or four-node cluster that requires two SCI switches

• Two-node cluster connected point-to-point

• Two-node switched cluster (degenerate case of the four-node cluster that allows for future expansion of cluster nodes with minimal interruption)

Figure 1-1 SCI Cluster Topology for Four Nodes

Figure 1-2 SCI Cluster Topologies for Two Nodes

SMA for Ethernet Clusters

Clusters of all sizes may be connected through a switch or hub. However, only two-node clusters may be connected point-to-point. The Switch Management Agent (SMA) software component manages communications over the Ethernet switches or hubs.

There are three basic Ethernet topologies supported in Sun Cluster (Figure 1-3 and Figure 1-4):

• Three- or four-node cluster that requires two Ethernet switches or hubs

• Two-node point-to-point cluster

• Two-node cluster with Ethernet switches or hubs (a degenerate case of the four-node cluster that allows for future expansion of cluster nodes with minimal interruption)

Figure 1-3 Ethernet Cluster Topology for Four Nodes

Figure 1-4 Ethernet Cluster Topologies for Two Nodes