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Question regarding performance of using differencing disks to quickly replicate identical servers

• Thursday, October 29, 2009 6:20 AMj2 Global

   
  

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  Hi All, I have a quick scenario that I would be gateful for any input :)
  
  I currently have 2 blade servers on which I hope to host 3-4 VMs.  All the VMs will be identically configured, and this configuration is more for load balancing than fail over protection.
  
  The problem is that the Hard Drives on the 2 blades are quite small: They are 72 GB.  I've currently got my vhd down to 30 (fixed), but even then I'm running into storage problems.  After installing the host server (even if the barebones hyper-v server r2), 60 gb vhds + HD space needed for RAM and potential snapshots literally drains all my HD space and I can't put more than 2.
  
  So I was wondering what kind of performance impact I would suffer if I were to make it so that all the VMs used differencing disks.  These would have a much smaller footprint and thus allow me to run all 3-4.
  
  Would 3-4 Diff VHD VMs be slower than running 3 full VHD VMs if they are on the same hard drive?
  
  How much, if any, performance gain or loss would I suffer if I were to put the master vhd onto a SAN, and only stored the differencing vhds (and vm configs) on the local HD?
  
  My ultimate goal is to minimize physical HD usage as much as possible without sacrificing too much in performance. 
  
  I would welcome any suggestions to help me achieve this goal :)
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