User guide

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

The I/O path policies supported since vSphere 4.x are as follows:

• MRU

– ALUA-aware

– Gives preference to the optimal path to the Vdisk

– If all optimal paths are unavailable, MRU uses a non-optimal path

– When an optimal path becomes available, MRU fails over to this path

– Although vSphere servers may use a different port through the optimal controller to access the Vdisk, only a single

controller port is used for Vdisk access per vSphere server

• Round robin

– ALUA-aware

– Queues I/O to Vdisks on all ports of the owning controllers in a round robin fashion, providing instant bandwidth

improvement over MRU

– Continues queuing I/O in a round robin fashion to optimal controller ports until none are available, at which time it fails

over to non-optimal paths

– When an optimal path becomes available, round robin fails over to it

– Can be configured to round robin I/O for a Vdisk to all controller ports by ignoring the optimal path preference

Note

Using round robin policy and ignoring the optimal path preference may be beneficial when you need to increase controller

port bandwidth to accommodate a write-intensive workload.

• Fixed

– Not ALUA-aware

– Subject to the same intricate configuration considerations as ESX 3.5 or earlier

– May result in a configuration where the non-optimal I/O path to a logical unit is used for I/O

– Not recommended for use with vSphere 4.x and an EVA array

• Fixed_AP

Introduced in vSphere 4.1, Fixed_AP I/O path policy extends the functionality of Fixed I/O path policy to active-passive and

ALUA-compliant arrays. Fixed_AP can also identify the preferred controller for a Vdisk.

Despite being ALUA-aware, the primary path selection attribute for Fixed_AP for ALUA capable arrays is the preferred

controller for a Vdisk and not just its access state.

To summarize, the key capabilities of Fixed_AP include:

– ALUA-aware

– Gives preference to the optimal path to a Vdisk

– Changes the access state of a Vdisk but not its PREF setting

– If all optimal paths are unavailable, Fixed_AP uses a non-optimal path and makes it optimal

– If all non-optimal paths are unavailable, Fixed_AP uses an optimal path

– If the path being used is non-optimal but preferred, Fixed_AP attempts to make this path optimal

• Although vSphere servers may use a different port through the optimal controller to the Vdisk, only a single controller

port is used for Vdisk access per vSphere server

– Starting with vSphere 5, the functionality of the FIXED_AP I/O path policy has been merged with the legacy Fixed I/O

path policy. So when connected to an ALUA -capable storage array, the Fixed I/O path policy in ESXi 5.x will behave like

Fixed_AP did in ESX 4.1 and revert to legacy Fixed I/O path policy when connected to non-ALUA storage arrays.