Servers/ hosts use multipathing for failover from one path to the other when one path from the Servers/host to the SAN becomes unavailable, the host switches to another path.
Servers/ hosts can also use multipathing for load balancing.
Types of policy:
Most Recently Used: The path used by a LUN is not be altered unless an event instructs the path to change. I will use this policy is for Active/Passive arrays and many pseudo active/active arrays. Most recently used (mru) selects the path most recently used to send I/O to a device.
Fixed: The path used by a LUN is always the one marked as preferred, unless that path is unavailable I use this policy is for Active/Active arrays. Fixed (fixed) uses only the active path.
Round Robin: Round robin (rr) uses the mru target selection policy and any HBA selection policy to select paths.
Custom (custom) sets the LUN to expect a custom policy.
