System information

n
Handles I/O queueing to the physical storage HBAs.
n
Handles physical path discovery and removal.
n
Provides logical device and physical path I/O statistics.
As Figure 2-3 illustrates, multiple third-party MPPs can run in parallel with the VMware NMP. The third-party
MPPs can replace the behavior of the NMP and take complete control of the path failover and the load-
balancing operations for specified storage devices.
Figure 2-3. Pluggable Storage Architecture
third-party
MPP
third-party
MPP
VMkernel
pluggable storage architecture
VMware NMP
VMware SATP VMware PSP
VMware SATP VMware PSP
VMware SATP
third-party SATP third-party PSP
The multipathing modules perform the following operations:
n
Manage physical path claiming and unclaiming.
n
Manage creation, registration, and deregistration of logical devices.
n
Associate physical paths with logical devices.
n
Process I/O requests to logical devices:
n
Select an optimal physical path for the request.
n
Depending on a storage device, perform specific actions necessary to handle path failures and I/O
command retries.
n
Support management tasks, such as abort or reset of logical devices.
VMware Multipathing Module
By default, ESX/ESXi provides an extensible multipathing module called the Native Multipathing Plugin
(NMP).
Generally, the VMware NMP supports all storage arrays listed on the VMware storage HCL and provides a
default path selection algorithm based on the array type. The NMP associates a set of physical paths with a
specific storage device, or LUN. The specific details of handling path failover for a given storage array are
delegated to a Storage Array Type Plugin (SATP). The specific details for determining which physical path is
used to issue an I/O request to a storage device are handled by a Path Selection Plugin (PSP). SATPs and PSPs
are sub-plugins within the NMP module.
VMware SATPs
Storage Array Type Plugins (SATPs) run in conjunction with the VMware NMP and are responsible for array-
specific operations.
ESX/ESXi offers an SATP for every type of array that VMware supports. These SATPs include an active/active
SATP and active/passive SATP for non-specified storage arrays, and the local SATP for direct-attached storage.
Each SATP accommodates special characteristics of a certain class of storage arrays and can perform the array-
specific operations required to detect path state and to activate an inactive path. As a result, the NMP module
can work with multiple storage arrays without having to be aware of the storage device specifics.
Fibre Channel SAN Configuration Guide
24 VMware, Inc.