Storage Path Automatically Reverts Back - RR to Fixed

[RussellFord]

Hello all. We are currently busy with a SAN storage refresh. All is going well so far and all vms have been migrated from our old IBM XIV SAN to the newly installed Dell Compellent SAN.

After having created the storage volumes and clusters on the Dell compellent I changed the storage path policy from fixed to round robin as this is the standard we have been using for the past few years and have confidence in. Around a week after having moved most of the vms to the newly created volumes we found the storage path policy on all the new volumes were once again set to fixed. I manually changed the policy back to RR for all the volumes. After having been out of the office for a few weeks I got back and checked the storage policy for all the new volumes. Sure enough they were all set back to fixed again. I checked with the team and confirmed that no one was changing this manually without me knowing about it. Event logs confirms this as well.

At the same time the old volumes on the IBM XIV no longer in use but still attached remains set to RR. The anomaly appears to occur only on the Dell SAN. Can anybody point me in the right direction here. I have not known vsphere settings to change by themselves historically. I have excluded human intervention and cant think that the Dell SAN would be responsible. The policy being a sphere feature. The only difference between the two SANs is that on the old one we aren't using storage clusters and on the new Dell we are. Anybody else come across this one before?

[sajal1]

HI RussellFord,

The path selection policy would be by default selected by ESXi unless you install any 3rdParty multipathing software. So physical paths maintained by you physical components. Logical path selection policy maintained by ESXi by default unless any other plugin is not implemented. So the path selection policy that were there for IBM may be different for Dell. You need to check the following:

First check the compatibility matrix for compatibility.

VMware Compatibility Guide: Storage/SAN Search

Second when you go deeper you would notice the default suggested policies by VMware for this particular type of storage

VMware Compatibility Guide: Storage/SAN Search

For example I took EMC and Symmetrix VMAX with FC as storage and vSphere 5.5 U1 as the OS. So it gives me the default values and what should be set if you use native multipathing, so for that the below was suggestion

Attention: Storage partners using ESX 4.0 or later may recommend VMW_PSP_RR for path failover policy for certain storage array models. If desired, contact the storage array manufacturer for recommendation and instruction to set VMW_PSP_RR appropriately.

Unless there is special instruction from Storage Vendor and if you are using the NMP then it should be followed.

To make matters easier ESXi always selects the default suggested one from VMware so if you are selecting the NMP then go ahead with the default policy that it selects. Shouldn't be any problem in that (unless special requirement from Storage Vendor).

For details check:

vSphere Storage Guide

Chapter 23: Understanding Multipathing and Failover 

vSphere 5.5 Documentation Center

So probably vSphere is reverting to the default best practices policy. Once you check the default suggested policy for Dell storage you can decide whether it is this or something else.

[guilherme_libor]

Hi

I have the opposite case, moving from Fixed to RR. I suspected the reason is the one you pointed. I have EMC Symmetrix VMAX and the default policy as stated on the compatibility guide is Round Robin (VMW_PSP_RR)

My problem is that i have an application running that requires Fixed path (don't ask me why i still didn't understand the reason from the supplier) and this is changing automatically to RR. Is there any way to overcome this and force the fixed path?

Thanks in advance