Hello,
I did some fairly intense research on netapp filers. The one thing that worried me was that issue of over subscription and WAFL. Here is what I found. When you use WAFL with snapshots and VMFS your active disk data blocks begin to frag across the array(s) and once the system snapshot volume saturates the array performance begins to degrade. This can be countered by running a defrag process but that interferes with the backup window (Or just add disk till the power outlet is cooked). If the array is oversubscribed it will need to flush the oldest snapshot pointers to free up raw blocks but again these are fragged and will not perform as well. One method of avoiding some of these issues is to use RDM and let snapdrive deal with snapshots.
Here is a netapp best practice guide you may find very usefull.
http://www.netapp.com/library/tr/3562.pdf
FYI
I'm still not sold on Netapp.
Seems to be priced much higher than many other solutions.
http://blog.laspina.ca/
vExpert 2009
