I see a couple of things that need to change.
The storage units are defined for one drive a piece when there are 2 of them:
Label: HCART-STU1
Storage Unit Type: Media Manager
Host Connection: nbu-media
Number of Drives: ...
Take a look at this article: http://www.symantec.com/docs/TECH124903
How big are the logs files that are not getting removed? Look at the bprd log to see if you are seeing the same messages the above article mentions.
It looks to be fixed with 6.5.6...
