jkgraham
Enthusiast
Enthusiast

Correct RAID type for storage of Virtual Machine Operating Systems

I have an environment looking at 50 virtual machines. 3 ESX boxes VMFS. The VM operating systems will be stored in ~12GB vmdk files. These VMDK files will only contain the OS and possibly the application installed (mostly SQL, IIS). No "data" will actually be stored on these vmdks. The site contents, databases and log files are stored elsewhere on the SAN.

The drives on the SAN will be 300GB 15K.

I am looking to put all these OS VMDKs on one RAID set either RAID5 4+1 or RAID 1/0 (6 drives). With the RAID5 I get the best bang for the buck, but feel the performance may suffer when getting 50-60 VMs. RAID 1/0 I use one more drive and loose more space due to mirroring, but get pretty good performance for small random writes.

The questions are: What kind of I/O characteristics should I expect out of just the OS and the application (hopefully not paging to disk)? Will there be a bunch of small random writes from 50-60 VMs? Out of the two RAID options above which would you guys recommend?

Thanks

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6 Replies
dkfbp
Expert
Expert

Hi,

You have 50 servers and they need 12GB each that is 600GB

Personally I would create a raid 1/0 which would give you 900GB of available disk space. Then divide this disk space

into 3 luns of 300GB each and host 16-17 virtual servers on each LUN. This would minimize scsi reservation issues and

give you good disk IO on your operating system drives.

It is also a viable solution to go for a RAID5 and hence have more disk space but lower performance. Both solutions will work

it is just up to you to figure out if you are OK with the loss of disk space in the raid 1/0 solution.

Best regards Frank Brix Pedersen blog: http://www.vfrank.org
jkgraham
Enthusiast
Enthusiast

Thanks!

The road you suggested is where I am leaning. I like the suggestion about dividing the LUNs across the RAID for scsi reservation concerns. I have googled plenty and reviewed the "Windows Internals" book and O'Riellys "Windows 2000 Performance" book but have not found much that discusses the base base I/O generated by the opeating system itself. Now, I am pretty sure this is somewhat dependent on what that operating system is being used for, but up for just the base OS I think the common I/O generated would be for paging to disk and any logging that needs to be done for general operation.

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petedr
Virtuoso
Virtuoso

I agree with what you are saying. In our environments we always go Raid 10 for alot of the same reasons.

There have been a couple of good posts on the forums discussing Raids and ESX, especially the discussions between Raid 5 and Raid 10.

http://communities.vmware.com/thread/92142

http://communities.vmware.com/message/532177

www.thevirtualheadline.com www.liquidwarelabs.com
jkgraham
Enthusiast
Enthusiast

Thanks all. Now to decide how many disks to eat up.

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petedr
Virtuoso
Virtuoso

thanks for the helpful, good luck with your environment

www.thevirtualheadline.com www.liquidwarelabs.com
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robertvirtualwo
Contributor
Contributor

Hi,

I would suggest NetApp's RAID DP (Double Parity/ Diagonal Parity).

VMware with NetApp storage has been said to be the best combination! Hope this helps.. RAID-DP offers significantly more protection than single parity schemes (including RAID 5 and NetApp RAID 4), with zero to minimal cost and performance impact. Compared to RAID 1 (mirroring), RAID-DP offers equivalent data protection against double disk failure at a fraction of the cost of mirroring. Compared to RAID 6, RAID-DP offers better performance and ease of use. Please excuse the brochure I added, it still has NetApp's previous logo, but if you'd like me to send you updated info don't hesitate to contact me or anyone else on the website.

Regards,

Rob ()(www.netapp.com)

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