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 PCIe flash. The HPP improves the performance of ultra-fast flash devices that are installed locally on your ESXi host. The plug-in supports only single-pathed devices.

Claim Rules

The PSA uses claim rules to determine whether an MPP or NMP owns the paths to a particular storage device. The NMP has its own set of claim rules. These claim rules match the device with a specific SATP and PSP.

The MPP claim rules are ordered. Lower rule numbers have preference over higher rule numbers. The NMP claim rules are not ordered.

Table 1. Multipathing Acronyms

Acronym

Definition

PSA

Pluggable Storage Architecture

NMP

Native Multipathing Plug-in. Generic VMware multipathing module.

PSP

Path Selection Plug-in. Handles path selection for a given device.

SATP

Storage Array Type Plug-in. Handles path failover for a given 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 flash devices.