Hello
My first suggestion is upgrade your DP version, let's go to say that 8.0 is not the best option please go to 8.15 or 9.06.
For to reclaim free space into StoreOnce first you must run omnimm manually.
Synopsis
omnimm -delete_unprotected_media [Library | -all]
Description
Manual removal of unprotected B2D backup objects
When invoked, Data Protector builds a list of unprotected backed-up objects residing in the B2D device. Data Protector first removes them from the store and then deletes the media information from the Data Protector database. Note that removing media from the store does not free-up disk space, it merely instructs the store to obsolete the data. You can optionally specify the name of the library. In this case only unprotected media from the specified library are deleted.
After that housekeeping process that run in background will release free space.
Removing unprotected B2D backup objects deletes the associated slots immediately. Deleting items does not free-up disk space immediately. During the next housekeeping job, expired files and unreferenced chunks are deleted, and possibly freeing up some disk space.
Best Regards