Multipathing is the ability of a server to communicate with the same physical or logical block storage device across multiple physical paths between the host bus adapters (HBAs) in the server and the storage controllers for the device, typically in Fibre Channel (FC) or iSCSI SAN environments. You can also achieve multiple connections with direct attached storage when multiple channels are available.

Multipathing provides connection fault tolerance, failover, redundancy, high availability, load balancing, and increased bandwidth and throughput across the active connections. Multipathing automatically isolates and identifies device connection failures, and reroutes I/O to alternate connections.

Typical connection problems involve faulty adapters, cables, or controllers. When you configure multipathing for a device, the multipath driver monitors the active connection between devices. Because multipathing is managed at the device level, when the multipath driver detects I/O errors for an active path, it fails over the traffic to the device’s designated secondary path. When the preferred path becomes healthy again, control can be returned to the preferred path. Multipathing prevents single points of failure in any highly available system.

A common example of multipath connectivity is a SAN-connected storage device. Usually one or more Fibre Channel HBAs from the host are connected to the fabric switch and the storage controllers are connected to the same switch. A simple example of multipath connectivity is: two HBAs connected to a switch to which the storage controllers are connected. In this case, the storage controller can be accessed from either of the HBAs that are providing multipath connectivity.

All OS platforms provide their own solutions to support multipathing. There are numerous other vendors that also provide multipathing applications for all available platforms, such as: