User guide

Technical white paper | HP Enterprise Virtual Array Storage and VMware vSphere 4.x and 5.x configuration best practices

Figure 16. Fixed_AP use cases.

Fixed_AP can cause explicit Vdisk transitions to occur and, in a poorly configured environment, may lead to Vdisk thrashing.

Since transitioning Vdisks under heavy loads can have a significant impact on I/O performance, the use of Fixed_AP is not

recommended for normal production I/O with EVA arrays.

Note

Fixed_AP can only be used to explicitly transition Vdisks on storage systems that support explicit transitions, such as EVA

arrays.

Fixed_AP can be leveraged to quickly rebalance preferred access to Vdisks after the configuration has become unbalanced

by controller failure/restoration or implicit transitions triggered by the storage and others.

Summary

In vSphere 4.x/5.x, ALUA compliance and support for round robin I/O path policy have eliminated the intricate configuration

required to implement multi-pathing in ESX 3.5 or earlier. These new features also help provide much better balance than

you could achieve with MRU; furthermore, round robin policy allows I/Os to be queued to multiple controller ports on the

EVA, helping create an instant performance boost.

Best practices for I/O path policy selection

• Round robin I/O path policy is the recommended setting for EVA asymmetric active-active arrays. MRU is also suitable if

round robin is undesirable in a particular environment.

• Avoid using legacy Fixed I/O path policy with vSphere 4.x and EVA arrays.

• In general, avoid using Fixed_AP I/O path policy with vSphere 4.x and EVA. However, this policy can be leveraged to

quickly rebalance Vdisks between controllers – for example, after a controller has been restored following a failure. This

use case can be employed with a single vSphere host when the array is not under heavy load. Once the balanced state

has been restored, you should end the use of Fixed_AP and replace it with a recommended path policy.

• Avoid using Fixed I/O path policy with vSphere 5.x and EVA. However since Fixed I/O path policy in ESX 5.x is the same as

Fixed_AP in ESX 4.1, the same use case considerations discussed above with ESX 4.1 also apply to Fixed I/O path policy in

ESX 5.x.

Configuring multi-pathing

The multi-pathing framework for vSphere 4.x/5.x includes the following core components:

• Native Multi-pathing Plug-in (NMP)

Also known as the NMM (Native Multi-pathing management extension module (MEM))

• Storage Array Type Plug-in (SATP)

Also known as the SATM (Storage Array Type MEM); used in conjunction with the NMP

• Path Selection Plug-in (PSP)

Also known as the PSM (Path Selection MEM); used in conjunction with a specific SATP