User guide

Technical white paper | HP Enterprise Virtual Array Storage and VMware vSphere 4.x and 5.x configuration best practices
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• Multi-Pathing Plug-in (MPP)
Third-party implementation (which is outside the scope of this document) that takes the place of the NMP/SATP/PSP
combination
Figure 17 outlines key components of the multi-pathing stack.
Figure 17. vSphere 4.x and 5.x multi-pathing stack
The key features of the multi-pathing plug-ins are as follows:
• SATP
The SATP is an array-specific plug-in that handles specific operations such as device discovery, the management of array-
specific error codes, and failover.
For example, while storage arrays use a set of standard SCSI return codes to warn device drivers of various failure modes,
they also make use of vendor-specific codes to handle proprietary functions and/or behavior. The SATP takes the
appropriate action when these vendor–specific return codes are received.
• PSP
The PSP selects an appropriate path to be used to queue I/O requests. PSP utilizes the following I/O path selection
policies:
– Fixed
– Fixed_AP
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– MRU
– Round robin
PSP settings are applied on a per-Vdisk basis; thus, within the same array, it is possible to have some Vdisks using MRU
while others are using the round robin policy.
• NMP
The NMP ties together the functionality delivered by the SATP and PSP by handling many non-array specific activities,
including:
– Periodical path probing and monitoring
– Building the multi-pathing configuration
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Only supported in vSphere 4.1