I sat in on an interesting session yesterday which gets under the covers of VMware performance on NFS datastores hosted on Celerra NS series. This was presented by a chap called Ken Cantrell who works for EMC engineering and was off the back of the fact that feedback from the field showed in many cases that some customers VMware estate simply wasn’t performing using NFS on Celerra. This is not the case for everybody, but it certainly was an issue. Essentially what was happening is the Celerra was dealing with an extensive amount of NFS calls to the UxFS log (predominantly Getattr type calls) and it was slowing down response types back to the host. EMC tested a workload on the Celerra using DART 6.0.4 using Jetstress. Jetstress effectively simulates exchange workload and also halts the benchmark if response times exceed 20 milliseconds on the basis of 20 milliseconds being to poor for a exchange. EMC were seeing that with the base version of DART 6 response time were exceeding 25 Milliseconds for the Exchange workload they tested on an exchange VM sitting on a Celerra hosted NFS datastore. EMC then released a patch upgrade which brought that down to sub 15 ms. EMC then released an experimental epatch (DART 126.96.36.1995 which brought response times down further to sub 10ms (closer to 6ms).
So bottom line is… don’t just suffer poor performance. Feed back to EMC if you see issues and also keep an eye on patch updates to the OS. They are there to resolve noted issues !
A good post on ECN with details of the new patch :
A good blog comparing iSCSI Vs NFS for VMware:
A good blog post by Jason Boche comparing the performance delta between Dart 6.0.4 and Dart 188.8.131.525