TheRealJason
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EMC PowerPath for RDM?

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I'm not even sure this is possible, but the question was posed to me by my boss today and I thought I should seek some knowledgable answers before I made a commitment one way or another.

We are planning on deploying some fairly heavy I/O applications in our ESX Cluster. SQL Clusters soon, and possibly Exchange in the future. We are planning on using RDMs to keep features like snapshots on our EMC device useful, and also to dedicate the load to a particular RAID group.

The question is, in this configuration, will VMWare still manage the paths to the SAN properly, or should we consider running EMC PowerPath inside the VMs? Initially, it doesn't seem to me like PowerPath would even work because it can't see the HBAs, but maybe there is something going on that I don't understand.

Has anyone else been asked this, or have thoughts on it?

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mreferre
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That is correct.

The policies (MRU or Preferred Path) used depend on the storage you are using. Usually MRU is used with mid-range storage servers with active/passive controllers.

Massimo.

Massimo Re Ferre' VMware vCloud Architect twitter.com/mreferre www.it20.info

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mreferre
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Jason,

you can't use OEM multi-pathing software within vm's simply because vm's do not have a clue they are running on a SAN (as you mentioned).

VMware is working to open the vmkernel interfaces so that storage oem's can plug into it their multi-pathing kits. As we stand right now (3.0.2) it is not possible.

Massimo.

Massimo Re Ferre' VMware vCloud Architect twitter.com/mreferre www.it20.info
TheRealJason
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Ok, thanks. So the MRU policy, assuming I haven't changed it, will still apply. I do not have anymore path redundancy, or any less, with an RDM than I would have normally.

In other words, the path is still being handled solely by the ESX server, regardless of whether it is a VMFS LUN, or a RDM LUN. Correct?

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mreferre
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That is correct.

The policies (MRU or Preferred Path) used depend on the storage you are using. Usually MRU is used with mid-range storage servers with active/passive controllers.

Massimo.

Massimo Re Ferre' VMware vCloud Architect twitter.com/mreferre www.it20.info
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TheRealJason
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Currently we are running an EMC CX-700 which has active/active controllers in it. At this level, is it usually recommended to set the paths ourselves? When do you determine whether to do that or not?

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Texiwill
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Hello,

Use MRU when you have a single active/passive SAN connected to an ESX Server. Use fixed when you have active/active or more than one active/passive SAN presenting to your ESX server. It is the number of active storage processors available on your fabric that present to an ESX server, If the # is > 1 use Fixed.

Best regards,

Edward L. Haletky, author of the forthcoming 'VMWare ESX Server in the Enterprise: Planning and Securing Virtualization Servers', publishing January 2008, (c) 2008 Pearson Education. Available on Rough Cuts at http://safari.informit.com/9780132302074

--
Edward L. Haletky
vExpert XIV: 2009-2022,
VMTN Community Moderator
vSphere Upgrade Saga: https://www.astroarch.com/blogs
GitHub Repo: https://github.com/Texiwill
mreferre
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Jason,

I am not familiar with the EMC kits. I know for example that the DS3000/4000 would use MRU and the DS6000/8000 would use Fixed (sorry ... the lable it's Fixed not Preferred Path). If you ask your EMC rep he/she will be able to assist.

Massimo.

Massimo Re Ferre' VMware vCloud Architect twitter.com/mreferre www.it20.info
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Texiwill
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Hello,

However if you had both on your fabric presenting to your ESX server then you would always used fixed. Sounds like the DS3000/4000 is active/passive and the other is active/active.

Best regards,

Edward L. Haletky, author of the forthcoming 'VMWare ESX Server in the Enterprise: Planning and Securing Virtualization Servers', publishing January 2008, (c) 2008 Pearson Education. Available on Rough Cuts at http://safari.informit.com/9780132302074

--
Edward L. Haletky
vExpert XIV: 2009-2022,
VMTN Community Moderator
vSphere Upgrade Saga: https://www.astroarch.com/blogs
GitHub Repo: https://github.com/Texiwill
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