Go to [URL] and click on Instructions > VNX Data Skew.  You'll get a script that will gather Sub-lun skew data from a VNX running OE 32. You'll have to run it through MiTrend and this is helpful to show the potential benefits of FAST to a customer who is not running FAST already as well as to validate the FAST value if they are running it already.  It's a very good complement to the NAR-based MiTrend Assessment.
I have a customer with VNX, but not running FAST at the time. Is there a way to analyze the potential benefits of FAST?
How can I know the skew of my VNX workload?