Users no longer able to back up to Time Machine volume

Question

Let me preface this thread by saying I have read Pondini's great Time Machine support page, and my issue seems most related to the #C4 topic, but it doesn't seem to cover the specifics of my situation. I have roughly 15 users at my company backing up hourly to a central storage device - an external 4TB  RAID 1+0 volume. It's one giant partition, and everyone has their own sparsebundle on it. Everyone is on OS 10.6.8. Backups went fine for the first half of the year, but eventually the TM volume filled up to about 99% capacity and started rejecting backups for multiple users. Rather than deleting old backups to make room for new ones, the backups simply fail now, with the "not enough space" error message on the client side.
As a band-aid solution I've been manually deleting the sparsebundles for users, and the backups resume for them as normal. Obviously this only solves the problem temporarily. I've also tried the method discussed in this forum about manually creating a 'dummy' sparsebundle for a user at a particular size, moving that to the TM volume, and then re-enabling backups - but this has never worked; the backups go way beyond the size I've set on the sparsebundle, and the TM volume continues to fill up. I know OS 10.6.3 changed the behavior of the sparsebundle's maximum size, so that's probably why my attempts to limit each user's maximum size has failed.
At any rate, one person suggested I create one partition per user on the TM volume, but this will result in seeing 15 different volumes available when connecting to it, which I'd like to avoid. If this is the only solution for me, though, I will reconsider it. I'm hoping there is another solution though.

Answer 1

steagl3 wrote:
Let me preface this thread by saying I have read Pondini's great Time Machine support page
Thank you very much. 
I have roughly 15 users at my company backing up hourly to a central storage device - an external 4TB  RAID 1+0 volume.
That is probably a lot of users for a single volume.   That works out to about 267 GB per user; as Etresoft says, Time Machine usually needs 2-3 times the space of the data it's backing-up, so if your average user has more than about 90 GB used, that may be the root of your problem. 
Backups went fine for the first half of the year, but eventually the TM volume filled up
If your users haven't added a great deal to their amount used since then, and roughly 6 months of backups is sufficient, you may have enough room.
Either way, though, all those sparse bundles are competing for the same space; if a few have managed to "hog" most of it, the others won't have enough space for new backups.  Since Time Machine will only delete backups from the Mac it's running on to make room, once the drive is near full, the size of any one sparse bundle usually won't change much. 
Since sparse bundles don't shrink when things are deleted, if something gets backed-up by mistake, deleting the backup won't gain any space.  The unused space will be used for new backups before it grows anymore, but you only recover space when the sparse bundle is "compacted" -- Time Machine will do that automatically when it's out of space, or you can do it manually (see the pink box in #12 of Time Machine - Frequently Asked Questions).
As a band-aid solution I've been manually deleting the sparsebundles for users, and the backups resume for them as normal.
That won't help much, since the ones with the problem are already too small; deleting one sparse bundle won't really help much. The new one will still be limited by the space taken up by the others.
If you do in fact have enough room, but some sparse bundles are taking up too much space, you might try deleting the big ones.  When a new backup has been done, try limiting the maximum size of that sparse bundle per #A8 in Time Machine - Troubleshooting  (rather than creating new sparse bundles yourself).  As noted, though, that doesn't always work.