This topic introduces the key concepts behind the ESXi storage multipathing.

Pluggable Storage Architecture (PSA)
To manage multipathing, ESXi uses a special VMkernel layer, Pluggable Storage Architecture (PSA). The PSA is an open and modular framework that coordinates various software modules responsible for multipathing operations. These modules include generic multipathing modules that VMware provides, NMP and HPP, and third-party MPPs.
Native Multipathing Plug-in (NMP)
The NMP is the VMkernel multipathing module that ESXi provides by default. The NMP associates physical paths with a specific storage device and provides a default path selection algorithm based on the array type. The NMP is extensible and manages additional submodules, called Path Selection Policies (PSPs) and Storage Array Type Policies (SATPs). PSPs and SATPs can be provided by VMware, or by a third party.
Path Selection Plug-ins (PSPs)
The PSPs are submodules of the VMware NMP. PSPs are responsible for selecting a physical path for I/O requests.
Storage Array Type Plug-ins (SATPs)
The SATPs are submodules of the VMware NMP. SATPs are responsible for array-specific operations. The SATP can determine the state of a particular array-specific path, perform a path activation, and detect any path errors.
Multipathing Plug-ins (MPPs)
The PSA offers a collection of VMkernel APIs that third parties can use to create their own multipathing plug-ins (MPPs). The modules provide specific load balancing and failover functionalities for a particular storage array. The MPPs can be installed on the ESXi host. They can run in addition to the VMware native modules, or as their replacement.
VMware High-Performance Plug-in (HPP)
The HPP replaces the NMP for high-speed devices, such as NVMe. The HPP can improve the performance of ultra-fast flash devices that are installed locally on your ESXi host, and is the default plug-in that claims NVMe-oF targets.

To support multipathing, the HPP uses the Path Selection Schemes (PSS). A particular PSS is responsible for selecting physical paths for I/O requests.

For information, see VMware High Performance Plug-In and Path Selection Schemes.
Claim Rules
The PSA uses claim rules to determine which plug-in owns the paths to a particular storage device.
Table 1. Multipathing Acronyms
Acronym Definition
PSA Pluggable Storage Architecture
NMP Native Multipathing Plug-in. Generic VMware multipathing module that is used SCSI storage devices.
PSP Path Selection Plug-in. Handles path selection for a SCSI storage device.
SATP Storage Array Type Plug-in. Handles path failover for a given SCSI storage array.
MPP (third-party) Multipathing Plug-in. A multipathing module developed and provided by a third party.
HPP Native High-Performance Plug-in provided by VMware. It is used with ultra-fast local and networked flash devices, such as NVMe.
PSS Path Selection Scheme. Handles multipathing for NVMe storage devices.