The multipathing APIs provide storage path failover, thereby optimizing storage I/O throughput and adding intelligence beyond the default pathing policies used by storage devices.
For a storage administrator to make use of vStorage APIs for Multipathing, the manufacturer of his storage system must have built support for VAMP into the storage system. vStorage APIs for Multipathing are coordinated in vSphere through a special framework in the VMkernel called the Pluggable Storage Architecture (PSA). The PSA acts as a base for two types of storage plug-ins: VMware’s Native Multipathing Plug-in (NMP) and a third-party vendor’s Multipathing Plug-in (MPP). NMP itself acts as a management layer for additional sub-plug-ins: Storage Array Type Plug-in (SATP) and Path Selection Plug-ins (PSP). These plug-ins make up VAMP. They decide which paths should be taken, monitor the health and state of each physical path used by storage I/O and activate inactive paths when needed.
VAMP was introduced in vSphere 4.0.