For some time now, I have noticed that when we make two complete system backups, the second set generally requires more tape media to complete. This is not noticeable unless the last tape of the first backup is nearly used up. So for example, if your first backup almost fills up 3 tapes, the second backup will require 4 tapes. I have known this for some time now. But when someone asked why, I was stumped. Can anyone explain this to me? Note: Our system backup routine just runs SAVSYS, SAVLIB *NONSYS, and SAV commands (basically an extract from option 21 of IBM SAVE menu).