Hi Michael,
Have you checked out the graphs in Performance Advisor ? You can downlaod the client from OpsMgr and all these coutners should be viewable and graphable (you can also check it out on much more granualr levels ie, Volumes/Luns)
Download from OpsMgr > Setup > Downlaod Management Console (follow the install and then login)
As off DFM 3.7 Perfadv also feeds certain reports to the native OpsMgr Reports - these are the Performance Reports - you can access these via Reports > All - Select Storage System Performance Reports from the left hand frame
Hope this helps
Rich