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I am planning to use a VMWare based setup consisting of two VMWare servers (2 CPU, 256GB Memory) and a DAS (DELL MD3220 with 24x900GB disks). The virtual machines will be half running MS SQL databases (Application, Sharepoint, BI) and the other half of the VM will be file services, IIS. To enhance the capacity of the storage, we'll be adding a MD1220 enclosure with another 24x900GB to the MD3220. Both DAS will have 2 controllers. Our current measured IOPS is 1000 IOPS average, 7000 IOPS peak (those happen maybe twice per hour).

We are in the planning phase now and are looking at the proper setup of the disks. The intention is to setup up both DAS one of the DAS with RAID 10 only and the other DAS with RAID 5. That will allow us to put the applications on the DAS that supports the application performance needs best.

Question is how best to partition the two DASs to get best possible IOPS/MBps, each DAS will have to have 2 hot spares?

For the RAID 5 Setup: Generally speaking, would it be better to have one single disk group across all 22 disks (24 - 2 hot spares) with both controllers assigned to the one disk group or is it better to have 2 disk groups each 11 disks, assigned to one of the two controllers?

Same question for the RAID 10 setup: The plan is: 2 disks for logs (Raid 1), 2 Hotspare and 20 disks for RAID 10. Option 1: 5 * 4 disks (RAID 10), with two groups assigned to 1 controller and 3 groups to the other controller Option 2: One large RAID 10 across all the disks and have both controllers assigned to the same group?

I would assume that there is no right or wrong, but it all depends very much on the specific application behaviour, so I am looking for some general ideas what the pros and cons are of the different options. IF there are other meaningful options, feel free to propose them.

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Just wanted to comment that I you want to go with a RAID solution using parity, I would suggest RAID50 over RAID5 for that number of disks –  Rex Dec 4 '12 at 14:41
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up vote 2 down vote accepted

Don't use RAID 5, as Rex says, or you are looking for a disaster. What ever you decide try to avoid a single poin of failure, read the storage documentation, or contact dell and ask them how to set up the controllers. Usually it will be active passive or ALUA. Make sure you have two HBAs in each of the servers, an this will allow you have redundant paths which is a good idea. I would be surprised if anyone reccomends dedicating a controller to a disk group. Dell should be able to give you good advice on this. As for your RAID setup, I am no storage master, but 10 and 6 is safe enough. Avoid 5.

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