FIGURE 11-1 illustrates SIMS running on a cluster. Each node in the cluster is a complete Solaris system with its own private disk that contains the operating system and the Sun Cluster software.
FIGURE 11-1 SIMS Asymmetric HA Configuration Before Fail-over
Since each node has at least one network interface connected to the public network, users can connect through this interface to read their mail messages. Each node has at least two additional private network interfaces, which connect to corresponding private network interfaces on the other members of the cluster. These are used by the Sun Cluster software on each node for system status monitoring and cluster configuration data sharing. Only one pair of private network interfaces is in use at any given time; the other is a redundant interface so that there is not a single point of failure.Each node has a connection to the disk cluster that contains the message store, message queues, directory contents, configuration files, and SIMS binaries. While both nodes are connected to the disk cluster continuously, the volumes in the disk cluster are mounted on only one of the nodes at any given time. FIGURE 11-1 and subsequent figures in this chapter show this disk cluster as a single logical volume.
Sun Cluster also includes the Sun Enterprise volume manager, which is based on the Veritas VxVM volume manager. The volume manager allows a logical volume to be mirrored across multiple physical volumes, providing uninterrupted service even if a physical disk fails.
As shown in FIGURE 11-1, only one of the nodes in the cluster runs SIMS at any time. This represents an Asymmetric High Availability (HA) configuration. In this configuration, all the SIMS binaries, configuration files, message queues, and message store reside on a shared disk. As a result, when a fail-over occurs the disk is unmounted from the failing system and mounted on the surviving system. FIGURE 11-2 shows the cluster after a fail-over.
The logical IP address is now configured on the public network interface of the other system. Users and mail agents on the public network always connect using the logical IP address. Thus, re-connecting after a failure automatically connects to the other system. A fail-over, will then, appear to be a very quick crash and reboot of a single system!
FIGURE 11-2 SIMS Asymmetric HA Configuration after Fail-over
In the SIMS Asymmetric HA configuration, the other node in the cluster is idle as far as SIMS usage is concerned. This node, however, remains a fully-functional Solaris system and is available for other work, as long as procedures to terminate or limit the other work after a fail-over are in place.As long as the CPU speed and memory size of the two nodes in the cluster are alike (recommended) in this Asymmetric HA configuration, the performance does not suffer during a fail-over. The stand-by node, however, is unused much of the time.