hi,  have a look at this, it might explain your situation.. we have seen it too: [URL]  sk
We have a new VNX 5600 installed last week.  I setup a single tiered RAID 5 pool for a VMware ESXi cluster.  I've zoned the ESXi servers, setup Host groups, and added the initiators to the host group.  The ESXi servers are seeing the storage appropriately with the appropriate amount of paths.  I allocated some LUNs to the host groups.  We configure the Virtual Machine Swapfile Location option on our ESXi servers to move the vm swapfile to a datastore LUN instead of them being located with the virtual machine.  We've created about 60 virtual machines in this cluster and the swapfiles for the virtual machines reside on the datastore LUN that has been configured.  None of the virtual machines are in production and they aren't doing anything right now other than just running.  VNX Monitoring and Reporting indicates that the response time for this LUN is very poor.  4 to 5 times an hour the response time will spike well over 20 ms (in the range of several hundred ms to 100 seconds).  I look in vCenter at performance metrics for virtual machines and the datastores and I see no latency issues for the datastore.  It's barely doing anything at all as far as read / writes.  In VNX Monitoring and Reporting there the iops is almost nothing.  Max iops reached 6 this morning and most the time it is a zero.  All the other metrics in VNX Monitoring and Reporting for the LUN in question are almost nothing also (queue length max .5, utilization is 0%, bandwidth is .0175, etc).  We have several other clusters configured the same way and the response time for the datastore LUN isn't having any issues so I'm wondering where the issue is?  Any thoughts?
lun response time (ms) very high