To maintain a constant connection between an ESXi host and its storage, ESXi supports multipathing. With multipathing you can use more than one physical path for transferring data between the ESXi host and the external storage device.

In case of failure of an element in the SAN network, such as an HBA, switch, or cable, the ESXi host can fail over to another physical path. On some devices, multipathing also offers load balancing, which redistributes I/O loads between multiple paths to reduce or eliminate potential bottlenecks.

The storage architecture in vSphere 4.0 and later supports a special VMkernel layer, Pluggable Storage Architecture (PSA). The PSA is an open modular framework that coordinates the simultaneous operation of multiple multipathing plug-ins (MPPs). You can manage PSA using ESXCLI commands. See Managing Third-Party Storage Arrays. This section assumes you are using only PSA plug-ins included in vSphere by default.