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IOmeter Cache only benchmark performance

Dear All
I am looking for some feedback regarding benchmark testing on our new Netapp FAS2552 running 8.2RC17 Mode 7 with Vmware using Iscsi  

I have connected the Netapp to Vmware ESXi 5.5 with a 10gb connection from the SAN to the switch and from the switch to the host.  I set up iometre to  test using using 4k blocks in sequential reads with outstanding IOPs at 16. I have limited the sample size 100mb, this effectively is making a cache run from the SAN and I have confirmed the read has 100% hit rate.
.  I am surprised to see that the maximum number of iop,s is only 20,000 with less than 90 MB-s being utilised.  I would have thought if the Netapp was serving 100% from cache memory the iop,s level would be significantly higher.  
I have also benchmarked against a LUN from the Netapp directly into the Windows 2008 OS using the software initiator within the Windows operating system.  I am seeing very similar performance.  Given the fact that everything is being served from cache, does it seem right for iop,s at this level?  Your thoughts would be greatly appreciated.