I think I get your point, but I think you misunderstand how it functions.     Say you have an empty external 500G (and I'll use round numbers for this example) hard drive you are using to store your media sets.   While the external drive is empty, if you create 3 new Media Sets to be located on that drive -- all 3 media sets will have a Capacity setting of 500g -- even thought it would be impossible to fill all three sets with 500G of data simultaneously.   If you back up 150G of data to each of those 3 sets, you will see that Used is 150G, but "Free" is still 350G -- for each set. But there's only 50G left on the external drive.   If you made three *new* sets at this point (using the default settings) the capacity of those 3 new sets -- would each be 50G only. Even if you tried to set the % to "100" -- it wouldn't let you use more than the available free space of the disk.     The Percentage "Use At Most" setting is *only* used when setting up the media set initially *or* when modifying the capacity of the Media Set by clicking the pencil icon in the Members tab for the media set to "resize" it.   "Use At Most" is not a *dynamic* setting (which is what I think you are thinking it should be, maybe?)     All I can say is that if the Capacity values for media sets changed between moving from 8.2 to 9.0 -- then I missed it entirely. It's been quite some time since I set up my media sets (most were set under 8.0 or 8.1), but all I can say is this is what my media sets look like:         and my external drive is a 4.5 TB RAID (with only 640G of free space on it). Which is why I groom some sets weekly and other sets monthly -- at this point I have a good handle of how much data I back up and how much data gets groomed off for my clients when I run grooms.       If I'm missing your point, then I apologize, but what I indicate above is how I've always seen it work.