I agree on that, start off with your local storage. If it hits 
the 120 MB/sec
ceiling, start highering your network bandwidth.
13 is a 
sh*tload of Windows guests, they need to be pampered with quite some
I/O. 
Using RAID50 might make up for not having SAS if you use enough 
drives.
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Sorry to hijack the thread, but is it only WIndows VMs that causes 
these problems?