I'm using a Time Capsule to do Backups, I've been doing this for a while now. The problem is that the backup begins small and with time it becomes huge. So restricting its size would make Time Machine use it's own space saving operations (I guess).

My idea would be to change the sparsebundle's size limit to a size much smaller than the hard drive's size. Since the sparsebundle is where the backups are done it should restrict available space and cause pruning when that limit is reached.

Would resizing the Sparsebundle cause any problem for the reliability or function of Time Machine?

  • 1
    Why do you need to manage the space the backup takes up? TM is perfectly capable of managing that on its own. – Marc Wilson Oct 31 '18 at 16:22
  • Hey @MarcWilson the thing is I would like to always have a certain amount of free space so I can use it without worrying about what TM has done. I use it to backup 2 computers. It's a 3TB Time Capsule and it's been backing up for a while so backups take up a lot of space. Deleting old backups (using tmutil) is a drag since it takes forever and also afterwards you need to free the space inside the sparsebundle using hdiutil compress. So it's just for convenience to avoid having to manually free space. – loco.loop Oct 31 '18 at 18:49
  • @MarcWilson Also... check this out: delete old backups and compress a sparse bundle. – loco.loop Oct 31 '18 at 18:55
  • ™ deletes old backups automatically when the disk runs out of space. – Mark Nov 1 '18 at 0:02
  • @Mark yes but the thing I want is to be able to have free disk space when I need it. If TM runs out of space it means also my Time Capsule has run out of space in which case I would have to do some manual cleanup... I would like to be sure that I will alwayse have some spare space to store whatever I want... – loco.loop Nov 1 '18 at 21:42

I much prefer to let the backup grow to take all available space if needed and just look at things when I set it up - maybe once every three days for a week or two then once a week or once a month till you are comfortable about the growth.

When I find there's something taking a lot of space and I don't want it backed up - say the iPhotos library on a portable when the master library is in iCloud and synced to a Mac mini at home - I don't need to back up the optimized version on the MacBook. Set Time Machine to exclude the library and then I go into Time Machine interface and select that library and use the gear control to delete all backups of that library file. (folder / package to be correct in the case of Photos).

This way, I have just the files I need backed up and no hassle guessing sizes before hand and restricting things. I always can get notified when the oldest backup gets cleaned and can see the space grow.

Lastly - I use a very slick tool that could help you analyze and alert you to large backup intervals.

You can do much of what it does manually with tmutil compare but I love the ease and graphs it provides.

  • This question isn't about setting up a new backup, it's about dealing with an old one. In my case Time Machine has filled a 2TB disk even though it's only backing up around 30GB of data (it's a work Mac that doesn't have any video/photos/music). I'm trying to recover some of that space to back up something else on the same disk. – Abhi Beckert Apr 15 at 0:09
  • Hi @AbhiBeckert - I understand sometimes you want to free up space instead of setting the drive aside. In practice, for me, it’s cheaper to set aside disks than spend hours cleaning. If you do want to clean, here are some tools to do that: How can I manually delete old backups to free space for Time Machine I absolutely don’t recommend cleaning from sparse bundles on TC - you could lose months of your life micromanaging that slow interaction. – bmike Apr 15 at 0:48
  • @AbhiBeckert Also - use my answer - BackupLoupe will analyze that 2 TB and tell you where it went. Then you could target remove all backups of X folder and reclaim your space. If you ever feel the time you are waiting for 2 Tb to delete, you’ll know how much a 2 TB drive costs and make the best use of your time and money and don’t need to trust my estimates / assumptions. – bmike Apr 15 at 0:51
  • there's no wasted space, the backup is large because Time Machine keeps a weekly backup going back as far as possible until the partition is full. I'm running tmutil delete to remove most of those (literally all of the data I care about is under version control anyway...). What I'd really like to do is resize the partition to be smaller, but I can't repartition because the disk is fragmented (HFS+ has problems with fragmentation on full disks). – Abhi Beckert Apr 15 at 1:31
  • You could ask a specific follow on question with your details. Your situation seems different enough than the one here to warrant it’s own post, @AbhiBeckert you could also put a bounty on the question here if you really wanted more answers to the one posed. – bmike Apr 15 at 1:34

From https://dongknows.com/this-trick-will-keep-time-machine-backup-storage-use-under-control/:

  • Determine the storage limit: Generally, 150% of the capacity of the Mac’s internal drive is a generous limit. Now convert that number in megabytes (MB).
  • sudo defaults write /Library/Preferences/com.apple.TimeMachine MaxSize CALCULATEDMAXSIZE

Once the backup file exceeds limited storage, old data will be deleted, so make sure you have a good choice of the limitation.

  • I saw the link and it seems fine though I haven't tested it... someone down voted this answer so I'm not voting or anything until I understand why they did it... why? – loco.loop Jan 7 at 19:21
  • The MaxSize setting was removed in Mac OS 10.13. – Abhi Beckert Apr 15 at 1:41

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