When I run Boot Camp Assistant, the attempted installation of Windows 10 fails, giving me the error "An error occurred while partitioning the disk." Have already tried First Aid on both my macOS boot volume and in recovery mode. Also tried /sbin/fsck -fy in single user mode. Both didn't work.

Here's the catch - when I make my own partition on my internal disk via Disk Utility (recovery mode and boot volume Disk Utility both have the same result) the partition will fail if I set the partition for over 15 GB. When I make a partition (not APFS container) that is 15 GB or less, Disk Utility will make it without problems. When I attempt to make a partition over 15 GB, the process will fail.

Now, A few days ago, I restored a Time Machine backup of my entire main internal drive via recovery mode and turns out that after that restore Macintosh HD reverted back to Mac OS Extended (Journaled) instead of APFS. After said restore and my internal disk being HFS, Boot Camp Assistant was fully successful in installing Windows 10. So I know that (hopefully) that process will work again if I want to install Boot Camp again. Since then, I deleted the BOOTCAMP partition and deleted Windows from my MacBook Pro (why I did that is a complicated story). I now want to re-install Windows 10.

However, I have an additional Time Machine backup of a clean High Sierra install which I restored to an additional APFS container on my internal disk just before writing this. When restored, this backup did not revert back to HFS after the restore, which in turn means bootcamp assistant/disk partitioning for 15 GB+ failed. I'm willing to restore the backup of my entire main drive from before all these shenanigans started in an attempt to get APFS to accept a partition, but I would like to know more options.

The main point - What are my other options to force APFS/High Sierra to accept a partition of greater than 15 GB and/or make Boot Camp Assistant actually go through with it's job. I’m open to all options to solve this problem. High Sierra has a lot of bugs in it and they're getting on my nerves. Apple needs to up their QC.

Anyways thanks to everyone for reading/helping me out - much appreciated :)

  • My first thought would be that you can not get more than 15 GB because that is all the free space available. Before a solution to your problem can be found, I would need you to post the output from the Terminal application commands diskutil list and diskutil apfs list. Most likely after you post the requested output, I will ask for additional command output. You can install Windows 10 without using the Boot Camp Assistant, but the procedure can be tedious. How much space did you want Windows 10 to have? Also, what is the model year of your MacBook Pro? – David Anderson Jan 7 at 19:03
  • I use a 13" 2015 MacBook Pro. My main macOS partition of my internal disk occupies 60gb at most (I can get it down to 50gb by removing some of my own files). My Mac has a 128gb SSD (121.12gb is what's actually available to use). No problem in asking for command output. I only need windows for very little, so 25GB will suffice. – Capt Inc 37 Jan 7 at 19:21
  • @David Anderson: Forgot this - since posting my question yesterday I made a TM backup, then completely wiped my internal disk, and was able to get Bootcamp Assistant to work and successfully install windows 10 with 35GB allocated to it. Am currently posting on a fresh install of High Sierra, but my intentions are to wipe this fresh install and restore my time machine backup from yesterday to my internal disk (when I can then post the output of the commands you asked for with my main disk/files). So that will have solved half my question, but I will still need to....continued in my next comment – Capt Inc 37 Jan 7 at 19:42
  • @David Anderson: my previous comment continued: ...."fix APFS/High Sierra to allow additional partitioning (not APFS containers) for my own reasons. I need future partitioning from macOS because I will need to restore a backup of my bootcamp partition at a later time. (or another option is to create a backup of my current bootcamp partition that can be restored directly to an APFS container created by disk utility which is then converted to FAT format by said backup) Thanks a bunch once again for your help, mate!! – Capt Inc 37 Jan 7 at 19:42

If your disk has been converted/formatted to use APFS, and you use Time Machine partitioning will typically fail because Time Machine made local APFS snapshots.

You can see the snapshots created with the command (use Terminal to enter it):

$ tmutil listlocalsnapshots /

If you see some, run the following command:

$ tmutil thinlocalsnapshots / 9999999999999

This last command will delete all the local snapshots.

Now run the Bootcamp assistant again, this time partitioning the disk should succeed.

  • Will getting rid of the local snapshots supposedly fix the issue at hand? What about completely disabling local snapshots with “sudo tmutil disablelocal”? Also I get the idea that only LOCAL snapshots are being a problem, and directing time machine to use an external disk only would prevent issues with partitioning from happening on the Mac’s main internal SSD. Is this true? – Capt Inc 37 Jan 20 at 16:11
  • Disabling Time Machine doest remove the local snapshots. So it will not help here. – jyavenard Jan 21 at 18:59
  • Ok so then that leaves deleting them via terminal. What about the local vs external backups thing? Only local snapshots are supposedly causing the problem, correct? – Capt Inc 37 Jan 22 at 19:35
  • local snapshots have no impact on your time machine backups, and obviously whatever backup you've made will have ZERO impact on your ability to resize a local partition. – jyavenard Jan 23 at 22:20

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