The Solaris I/O multipathing features select the best paths to access Oracle FS System LUNs.
Path optimization state
Path performance
Path availability
The path optimization state depends on whether the LUN is currently homed on the Controller to which the path is connected. An optimized path is a path that connects through the Controller where the LUN is resident or homed. A non-optimized path is a path that connects through to a Controller where the LUN is not resident (homed) on the that Controller. Optimized paths are always preferred, but if an optimized path is not available, the non-optimized path is used temporarily for I/O traffic.
Path performance is determined by how quickly and reliably a path transfers I/O traffic to and from a LUN.
Path availability is determined by the ability of the path to transfer I/O traffic. An available path is fully functional; however, if the path stops working, the path is considered unavailable.
These factors determine how the paths to each Oracle FS System LUN are divided into groups.
For each LUN, the currently configured load balancing algorithm is used to select paths from the most preferred group that has paths available. Only paths from a single group are used at any one time.
When an active path fails, I/O traffic is transferred to a different path. I/O performance is reduced for a short time while the operating system recognizes the failure and makes the path transfer. After the path transfer is complete, I/O performance improves.
If the failed path is optimized and the new path is non-optimized, I/O performance can continue to be reduced after path transfer because a lower-performance path is in use. Within a few minutes of traffic being transferred to a non-optimized path, the Oracle FS System attempts to move the LUN to the appropriate Controller for path optimization. After transfer to an optimized path succeeds, I/O performance improves.