What is MPIO?
MPIO is an acronym for MultiPath Input Output. This is a framework that gives administrators the ability to configure load balancing and failover processes for connections to storage devices. Most storage arrays offer this in the form of multiple controllers, but the servers still need a way to spread the I/O load and handle internal failover from one path to the next. This is where MPIO plays a key function, because without it servers would see multiple instances of the same disk.
Multipathing solutions use redundant physical path components like adapters, cables, and network switches, to create logical paths between the server and the storage device. In the event that one or more of these components fails, causing the path to fail, multipathing logic uses an alternate path for I/O so that applications can still access their data. Each network interface card or HBA should be connected by using redundant network switching to provide continued access to storage in the event of a failure.
New MPIO features in Windows Server 2008 include a Device Specific Module (DSM) designed to work with storage arrays, and are included with most of the Dell Storage products.
The Microsoft DSM provides the following load balancing policies. Note that load balance policies are generally dependent on the controller model (ALUA or true Active/Active) of the storage array attached to Windows-based computers.