Resource Hierarchies - SIOS

Communication Path Types
• Safety check. If all comm paths die, SPS performs a safety check to verify system failure
before switching over resources.
Communication Path Types
SPS 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. SPS uses the paths in
priority order for inter-node communication. However, SPS sends heartbeat signals over all active
comm paths. These are the comm paths supported by SPS 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, SPS uses the comm
path with the highest priority for communicating resource status.
• Shared disk. SPS 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 SPS 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.
CAUTIONS:
• An SPS 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.
SteelEye Protection Suite for Windows 5