You have already 1 and 0 on your Iseries disks and of course.
The Iseries are not little games as some PC. They use a lot of complex technologies as Mirroring and Raid 5 to manage there disks. So let them do it.
The way to clean the Iseries storage is :
1) Delete unused files
2) Reorganize files by files (RGZPFM command)
See RedBooks or IBM publication on UDB for that.