I'm not sure why you'd say "this looks like an XVS model" when I clearly stated the model was a PS6100XS. The explanation I got from Dell was: "The SAN’s performance is such that the write cache is not being utilized at all because the disks can handle the performance without caching.  While you are seeing your SSD drives being outperformed by your 10K, that is only because performance wise and where the capacity lies, the 10K may have more of the data and can handle the access to it." and that makes sense to me.
  [IMAGE] I think the picture (from SAN HQ) speaks for itself. Can you anyone tell me why our SSD drives are slower than our 10k drives in average IOPS as well as Read/Write I/O rates? The measurements reflect the last week of activity. We're on firmware 5.2.1 
SSD performance slower than 10k drives in PS6100XS