This is more of a hypothetical question, but we've been using a Time Capsule to back up our Macs, and it has steadily been filling up since the year or so that we've had it.

We've since brought a few new Macs onto the network and have started backing them up to the Time Capsule as well. From what I've read, Time Machine makes incremental backups of Macs, and apparently deletes old backups to make room for new ones.

My question is twofold:

  1. How does Time Machine decide which backup information to delete, especially amongst several Macs backed up to a single Time Capsule?

  2. As we add more users to the Time Capsule, and it begins to fill, will Time Machine be smart enough to give new users enough space by deleting old backups from other users? If not, how can we achieve this?

  • 1
    Your question is actually two questions. I've deleted the second part. Please start a new question for this..
    – Rob
    Commented Mar 19, 2014 at 19:05
  • Fair enough. I'll do so.
    – Argus9
    Commented Mar 19, 2014 at 20:45

1 Answer 1


My experience is that TimeMachine does not cross the "per-machine" boundary when deleting old backups.

We have a disk attached to an AirportExtreme AC and which is the target for four Macs. These machines have significant differences in the size of their backups. One of them in particular is an old Mini running 10.6.8 that does not see much activity other than the occasional software update, so the incremental backups are rather tiny. The MacBook Pros on the other hand are a lot more active and regularly submit incrementals that are several GB in size.

Whenever the MacBook Pros need space TM just discards their own history, never touching the others' directories.

This fact is immediately evident when comparing the number of backups for each machine. The Mini has a long history saved, the MBP's quite shorter ones. Hope it helps.

  • I feel like we're dealing with the same issue. I've thought about using OS X Server as a Time Machine and applying a quota to each user, and planning ahead of time how much space to allot to each user. Time Machine might handle a lot of the footwork on its own, but at least Server lets you have a certain amount of control of your backups. :)
    – Argus9
    Commented Mar 19, 2014 at 20:47

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