I am moving several hyper-v VMs from an under-powered host to a newer host with an iSCSI array for storage. What is the best configuration for the iSCSI volume to get the best performance for hyper-v? Should I make one large LUN and then just put all the vhds on that LUN or would multiple smaller LUNs work better with hyper-v?

The host server is a Dell r710 with dual NICs dedicated to iSCSI with the Dell MPIO drivers installed. The MD3000i is using all iSSCI ports through the same physical switch as the r710.

Most of the servers are self contained machines and the disk I/O is not heavy for most of the machines. I do have three development servers that work as build target machines which have higher disk I/O than the other serevrs but the builds are not constantly running.


It really depends on the SAN, connectivity, and workload. For a single server it should be sufficient to have a single LUN. RAID10 will get you the best performance, though with the caching on most SAN devices RAID5 you'll usually not notice the performance penalty.

The biggest difference is if you use one big LUN for all the VMs is that you can use dynamic VHDs, software snapshotting, and differencing VHDs. Using individual LUNs will yield better performance all around and allow you to use hardware snapshotting. Usually the former's benefits outweigh the latter. Most commonly the high performance VMs (SQL, etc) get passthrough LUNs and everything else shares a CSV.

  • The SAN volume is RAID 10. I was looking for experience of a single large LUN basically being a file volume that the VHDs reside on vs. having multiple LUNS (on for each VHD) all presented to the host and mounted for hyper-v to see. – Top__Hat Nov 11 '11 at 0:45
  • This is what I was looking for. The dedicated SQL boxes are all on separate hardware so I'm already covered there. I just need to get some legacy hardware shut off and a bigger LUN for for all the VHDs seems like it will work fine. If a machine seems to be having I/O issues I can always move the VHD to a new LUN during maintenance. – Top__Hat Nov 11 '11 at 3:03
  • You can't concatenate multiple smaller LUNs together with hyper-v? I know you can with VMWare... – Basil Nov 14 '11 at 18:39

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