When the Red Hat Enterprise Virtualization Manager discovers all of the connected LUNs, multipathing is defined over the storage network. All valid paths between the LUNs in the network are mapped and consequently alternate paths are defined in case the primary path fails.
Multipathing protects against a single point of failure and provides increased bandwidth and improved security within the network. All volume groups are created on top of multipath devices, even if multiple paths are not defined for a given device.
Multipathing provides:
Redundancy
Multipathing provides failover protection. If any element of an I/O path (the cable, switch, or controller) fails, an alternate path is found.
Improved Performance.
Multipathing spreads I/O operations over the paths. By default this is done in a round-robin fashion. However, other methods are also supported, including for example
Asynchronous Logical Unit Access (
ALUA).
In this configuration, there is one I/O path that goes through hba1, SAN1, and controller 1 and a second I/O path that goes through hba2, SAN2, and controller2. There are many points of possible failure in this configuration:
A failure at any of these points will cause a switch to an alternate I/O path.