Vsphere 4.1 fixed vs round-robin

[jedijeff]

I am in the process of moving our 3.5 cluster to a new 4.1 cluster. I am almost down presenting all our hitachi 9985 storage to the new 4.1 cluster, and I had manually load-balanced the hba's/luns with a Fixed policy. Primary as that was the default plugin that came up.

Then it just dawned on me this round-robin policy. Is this supported for all active/active arrays? or only ones with AULA?

I am assuming our 9985's are true AA and each SP can access the lun with no ping-ponging at all. If that is the case,,,than wouldnt round robin be a far more efficient way for me to balance the hba's and luns on a host?

Thank you.

[admin]

Actually Round-Robin support both A/A and A/P array. If the device have multip "Active" pathes, ESX will balance the I/O between all the "Active" pathes.

So, yes, it is a good way to balance the I/O between HBAs and SPs.

[MKguy]

Check which SATP ESX detects to use for your array, each SATP has a default PSP like fixed, MRU or RR. The default SATP/PSPs are also listed on the HCL for each storage array.

If your array supports ALUA, then ESX should default to the generic ALUA-aware SATP called VMW_SATP_ALUA which uses MRU as the default PSP. If your storage array or vendor supports RR too, you should be able to safely change the PSP to RR. You might want to set a custom IOPS limit for RR too.

Here are some more infos for HP EVA arrays, which are AA and support ALUA with RR:

http://www.ivobeerens.nl/?p=465

[admin]

We do not need array to support RR.

Please refer to KB1011340, http://kb.vmware.com/kb/1011340

"

VMware does not recommend changing the LUN policy from Fixed to MRU

as this policy is based on the array that has been detected by the NMP

PSP.

Switching to Round Robin is safe and supported for all arrays.

"

[thakala]

Yes Sun 9985 (it is HDS NSC55 actually) is true active-active array, but it doesn't matter as VMware round-robin PSP works with any storage type.

Since you have active-active storage you really should consider procuring PowerPath/VE, it is supported with 3rd party active-active arrays, we are using it with 9985 and performance increase over round-robin PSP is quite awesome. Even without performance increase it would be very good purchase because with PowerPath/VE SAN and Storage port load is truly balanced evenly, which VMware PSP does not guarantee.

[jedijeff]

Thanks everyone for the information. I set one of my hitach luns to RR and I can see in esxtop the cmd/s are being balanced.

I read somewhere-cannot find the link now-that when using RR you should adjust some IOPs paramater on the host that it uses for the balancing? Anyone know the link or paramater I am speaking of?

Thanks!

[MKguy]

If you would have read the link I posted earlier or did some googling youself, you would easily have found it yourself.

Anyways, the basic command is:

esxcli nmp roundrobin setconfig --type "iops" --iops=X --device Y

For switching paths every X IOPS on device Y.

You should check with your storage vendor if that is actually recommended. HP for example recommends it in their whitepaper.

[jedijeff]

I am sorry I missed that link, and in fact that is the link I had found googling last night. Thanks!