Virtual Disk on VMware - RDM or VMFS for your SQL Server

Just curious for those using VMware if you present RDM's or utilize VMFS for your storage to your SQL Servers. Traditionally we have used RDM but as we are growing our Virtual SQL environment, this is presenting challenges with the number of host and guest and wanting to utilize DRS (vmotion). Just wanting to get a feel from others out there with a bit more experience than myself. Since we utilize and enterprise SAN and all disk basically come from the same pool or are carved out of the same array's then as long as my throughput and IOPs are consistent I don't see a big problem.

So guys and gal's, PRO's and CON's. Success and horror stories, let them rip.

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asked Aug 14, 2012 at 03:12 PM in Default

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I'd be interested in hearing about this. I've just been peripherally aware of virtualization of storage and understand it to be "a bad thing" but I haven't heard much about the why's & wherefores.

Aug 14, 2012 at 03:17 PM Grant Fritchey ♦♦

I had dinner last night with a guy who wrote the white paper on it. I plan to hound Jonathan K about it today during training. Any info I get from them I will email to you.

Aug 14, 2012 at 03:19 PM Tim

@Grant Fritchey Both Jonathan and David Klee have told me to read this document from VMware where the recommendation is VMFS over RDM. The few exceptions are if you think you might want to migrate the luns from VM back to physical or if the IO load requires a different set of disk.

I too was under the impression from others that VMFS was not recommended for SQL. Guess we both listened to the same session. :)

Aug 15, 2012 at 06:50 PM Tim
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I have a 5 cluster ESX setup at the moment, and I'm a big fan of VMFS. It's quite close to RDM in terms of performance, but it gives all of the high availability options that you can't have with the RDM such as failing VM's across sites (without SAN replication and other expensive toys). Also you can expand the partitions much easier if you find you need more space, whereas that can be a pain (or potentially not possible) using RDM.

If you find the VMFS too slow, try RDM, but I'd almost go for a physical machine over having to use RDM's due to the impact they can have on HA. I would also add that thin provisions on VMFS can be a bad idea, especially for DB servers. Make sure you thick provision and just expand if you need it, having the file grow during an operation, combined with the potential fragmentation across the physical disks, is a recipe for disaster.

Purely opinion, but just my two cents. Good luck!

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answered Aug 14, 2012 at 03:31 PM

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asked: Aug 14, 2012 at 03:12 PM

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Last Updated: Aug 15, 2012 at 06:50 PM

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