SIOS Protection Suite provides three different types of comm paths so that you can define redundant comm paths using different protocols. Although there is less value in defining multiple paths of the same type over the same media, redundant paths using different protocols or different media provide good protection against failover due to a comm path failure.
When you define your comm paths, you establish a priority for each path. SIOS Protection Suite uses the paths in priority order for inter-node communication. However, SIOS Protection Suite sends heartbeat signals over all active comm paths. These are the comm paths supported by SIOS Protection Suite and the default priority range assigned to each:
- TCP/IP (socket). The LAN comm path is given the highest priority. The default priority range for the socket path is 1 to 30. You can define multiple LAN comm paths between a pair of servers by defining each one over a different adapter to prevent false failovers.
Note: The LifeKeeper GUI uses TCP/IP for communicating status information about protected resources; if there are two TCP/IP comm paths configured, SIOS Protection Suite uses the comm path with the highest priority for communicating resource status.
- Shared disk. SIOS Protection Suite allows you to define a raw disk partition on a shared disk as a communication location for a pair of servers in the cluster. The shared disk path must be identified with the same drive letter on both servers and the drive letter must identify the same disk partition. The disk partition is usually small, typically one megabyte. The default priority range for the shared disk comm path is 61 to 99 (not supported in greater than two-server configurations).
Note: Shared Disk comm paths are used by SIOS Protection Suite only for detecting whether other servers in the cluster are alive. Therefore if the TCP/IP comm path used by the LifeKeeper GUI is down, the GUI will show hierarchies on other servers in an UNKNOWN state, even if the shared disk or secondary TCP/IP comm path is operational.
More About the Shared Disk Comm Path
The shared disk comm path can be used as a channel of last resort in the case where all other communication has been severed. If the shared disk comm path were to be lost as well, it is very likely that at least one of the servers would not be able to access the storage subsystem, thereby preventing a “split-brain” situation where both servers may access the same disk resource simultaneously.
- A SIOS Protection Suite configuration should include no more than one shared disk comm path between any two servers in the cluster.
- Before using shared disk comm paths on JBOD or Host-based RAID, be sure to test the comm path for reliability when a member of the cluster is shut down or out of service. Sometimes, in configurations using JBOD or Host-based RAID, the comm path will fail to go down when a cluster member goes down, and therefore a failover is not initiated.