Christoph,
I found a workable solution after a day or worth of digging around with google.
1) I use tw_cli to review the status of the controller's drive manually when needed via ssh
2) John's blog below has a very useful approach that send an automated email on drive isssues. I have not gotten the script to work yet (currently errors) but I am on 5.0 and not 5.1. I will fix the script when i upgrade to 5.1 as for now being able to use tw_cli is much better than my situation a few days ago.
http://www.joshwesley.com/2013/03/vmware-esxi-51-raid-email-alerts.html
Cheers,
neo