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I have a ~500GB Time Machine partition I'd like to shrink slightly. My internal source partition is around 400GB.

Resizing the partition would be extremely slow, since Disk Utility has to check all the hard links Time Machine is using behind the scenes. On the other hand, simply wiping it and backing up again from scratch would also be extremely slow.

Is one or the other generally going to be faster? Is there some disk size tipping point at which it becomes more economical to switch strategies?

(I'm using an SSD internally and a spinning hard drive externally, connected over USB 3. Both the source and the destination are encrypted. Also, I have a second backup disk, so if I wipe and back up again I won't be temporarily unprotected.)

SilverWolf
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  • In an ideal situation, your time machine drive should be bigger than your startup drive. Some people say 2 and a half times bigger. Time Machine collects as many backups of a file as it can. At one point, I noticed some missing data in a file. I had to go back 9 months to find the missing data. This is the feature of time machine that you will eliminate by strangling time machine's drive. – historystamp Dec 08 '18 at 21:11
  • I'm not sure you will be able to use drive resize. I think time machine will fill up the drive with backup files. There will be no free space for disk utility to reclaim. The terminal command df -h will let you know how much free space there is on all your drives. – historystamp Dec 08 '18 at 21:15
  • Thanks. Yeah, I know I should probably make it a little bigger. My other backup drive has another partition on it that I'm not using, so I could probably grow the other TM partition to 600GB (and I back up onto it less often). I really just need to shell out for a bit more storage. Games are far too big these days! (: – SilverWolf Dec 08 '18 at 21:15
  • I've deleted the older backups with tmutil delete, which gave me quite a bit of space. – SilverWolf Dec 08 '18 at 21:15
  • I use time machine for accidentally deleted or mangled files. I use carbon copy cloner to make a bootable backup of my system. I think super duper offers free cloning. "Clone, synchronize, backup. Schedule and forget it." http://www.bombich.com/software/ccc.html

    "SuperDuper is the wildly acclaimed program that makes recovery painless, because it makes creating a fully bootable backup painless." http://www.shirt-pocket.com/SuperDuper/SuperDuperDescription.html

     – historystamp Dec 08 '18 at 21:19
  • SuperDuper looks really nice, not that I really need a bootable backup. (: I have had some issues with Time Machine not saving quite everything, though, like ~/Library/Screen Savers (which I have lots of Quartz compositions in). – SilverWolf Dec 08 '18 at 21:23
  • A bootable backup is great. You will be in panic mode if your startup drive fails. My machine was acting crazy a while back. I booted from a backup drive. I proceeded to wreck the backup drive. I had to go to my second backup drive :-(. You can do a test boot from the backup drive. I don't like to rely on backup that are a hassle to test. – historystamp Dec 08 '18 at 21:24
  • From my experience (2/2 times), shrinking TM partition corrupts the filesystem. TM might not backup and First-Aid reports error (and unable to fix). – amdyes Dec 10 '18 at 08:13
  • @amdyes Huh. It worked fine twice for me, then failed on the third time (once with one partition, then twice with a different partition). I ended up blowing the second partition away and I'm now backing up again from scratch. I didn't bother trying First Aid. I was using diskutil cs resizeStack instead of Disk Utility, though. – SilverWolf Dec 10 '18 at 16:15

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Unfortunately, I cannot give a catch-all answer. So my suggestion is to resize the partition, and, chances are that that may be faster. But if I'm being truthful, there are too many variables to determine which method would be objectively better at which sizes and such. Sometimes, these things will just take their time and no matter how you do it, you will be spending a significant amount of time waiting, so yes. Just choose a method and wait it through.

Henry7720
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