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I'm spec'ing a server to be used as a virtualization platform. What's the best RAID configuration to use on that type of server?

I've read the RAID 5 is not a good choice for hypervisor situations (probably due to the poor random write performance).

The controller would be a PERC 6/i SAS RAID controller.

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up vote 3 down vote accepted

We have a Poweredge 2950 running Hyper-V with a six disk RAID5 and there are no performance problems. This only runs ten VMs, so you could argue that it's not that heavily loaded, all the same the disk performance is very good. Very, very good in fact!

People seem to have a real downer on RAID5, and it's certainly true that if you have the array configured for write-through the write performance is poor. However the Perc 5/i and 6/i controllers seem to manage write caching very effectively and unless your system is doing an awful lot of writes I doubt disk speed would be a problem. Yes, RAID10 will be faster, but that isn't the same as saying that RAID5 is too slow.


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I'll have to weigh the cost difference (number and size of drives needed) between RAID 10 and 5, but I'm glad to know that RAID 5 is a viable option. – Chris Thompson Jul 8 '09 at 21:42

RAID 10 will give you speed and redundancy, but at a higher cost. RAID 5 is considered slow for virtual infustructures and databases.

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To clarify - the question asked for the best, and RAID 10 is the best, so +1. – Brent Ozar Jul 8 '09 at 1:20

RAID10 should offer the performance and redundancy you're looking for. Here's an article (albeit a little old) regarding it:

I double-checked the specs on the controller and it should support RAID10 just fine.

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Whatever you decide, please remember that RAID 0 is not really RAID because there is nothing redundant about it.

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That goes without saying! (I run RAID 0 on my home computer for the OS, but I like to run on the wild side) – Chris Thompson Jul 7 '09 at 20:55

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