What version of vSphere are you currently running? VMware KB: Intermittent NFS APDs on VMware ESXi 5.5 U1 - this was patched, you should apply the appropriate level of patching. I don't see anything wrong with this configuration. However ideally, if you have unified storage it is probably best to present it directly from the storage.
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vfk
Systems Manager / Technical Architect
VCP5-DCV, VCAP5-DCA, vExpert, ITILv3, CCNA, MCP