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Installed windows 10 via bootcamp on my MBP running macOS Sierra, but I'd like to expand the Windows partition and shrink the macOS partition, avoiding a reinstall if possible.

I did a search already, but the other questions I've found on this topic are 1) about windows 7 and 2) just suggest using WinClone or similar.

How would this be done manually without the use of paid utilities?

Edit: I've used gParted from an ubuntu live USB to resize the windows partition. The only issue now is that windows throws an error on boot. Online sources suggest using gdisk to somehow sync the GPT and MBR tables?

(I have data backups and mac OS boots fine, so now it's just a matter of curiosity and avoiding a reinstall if possible)

  • 1
    Welcome to superuser: gparted (if still free) is a very good partition software disc. It may aid you to checkout software rec's at 'softwarerecs.stackexchange.com/questions' again welcome to superuser. – mic84 Nov 20 '17 at 23:30
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Ok, here's how I solved my problem in the end (resizing a windows 10 bootcamp partition):

Shrinking the macOS partition

  1. Boot into recovery mode and open terminal
  2. Run diskutil cs list to list core storage logical volumes, and copy the Logical Volume UUID
  3. Resize the logical volume with diskutil cs resizeStack LVUUID size where size is a parameter such as 80g (80 gb)

Expanding the Windows partition

  1. Create an ubuntu live USB using this tutorial
  2. Boot into the ubuntu live USB (hold option on boot up to select)
  3. Open GParted and use it to expand the windows partition into the free space created earlier

Fixing the MBR so Windows boots

This method seemed to work, I don't know if it is correct practice but Windows does boot now.

  1. Boot into mac OS and install gdisk (download the .pkg file and install)
  2. Open terminal and run diskutil list, make note of the startup disk identifier (/dev/disk0, /dev/disk1, etc)
  3. Run sudo gdisk disk_id replacing disk_id with the identifier from the previous step
  4. Type x to enter expert mode
  5. Type n to create a new protective MBR
  6. Type w to save the changes and confirm with y
  7. Reboot into Windows!

A final note of caution

I had backups of all of my important data in case something went terribly wrong and I was forced to re-install windows, macOS or both. Do not attempt this without backups of your data!

Be warned that I am no expert and put together this procedure with information from existing discussion board posts, so what worked for me may not work for you.

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Don’t ever touch the partitioning from Windows!
No Windows app can figure out how it is being ‘fooled’ into thinking it’s in charge.

There are only 2 apps that won’t simply break Boot Camp completely, Paragon Hard Disk Manager & TwoCanoes WinClone. afaik, neither can yet handle APFS.

Carbon Copy Cloner can safely back up HFS & Boot Camp partitions, but cannot by itself recreate them, you must complete the underlying formatting first.

Apple’s own Disk Utility will not allow you to even attempt this. The Apple-recommend method is to completely remove Boot Camp & start over with a bigger partition size.

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  • What makes it technically impossible to enlarge the APFS first and then do so with the virtual partitioning underlying in two separate steps with specific tools for each? Is Disk Utility the only software capable of handling APFS? After reading your questions published here I dont think you're a power user, so I dont think you should deliver "nos" around so easilly... – DGoiko Nov 21 '17 at 19:15
  • I spend most of my time on Ask Different, where “I resized my BC partition & now it no werky” crops up with alarming regularity. There is one guy on there who could knit you a new hard drive in Terminal if you gave him the wool. For mere mortals, prudence & correct tools would save a whole lot of grief... & that’s without the huge added complexity of APFS. – Tetsujin Nov 21 '17 at 19:34
  • okey, then I got you wrong. I understood impossible, instead of not recommended for begineers. I'll retire the downvote then, just edit your answer and add a dot or something so it will allow me to withdraw the downvote – DGoiko Nov 21 '17 at 19:38
  • I made an edit. tbh, it’s not just beginners who ought to avoid attempting this by hand. Seasoned pros would give it a wide berth. Look up answers by klanomath on AD to see what can be involved. Personally, with nearly 30 years’ experience, I would still buy the right tools. It’s just too easy to get wrong. No animosity intended at all, I’ve just seen far too many people fail badly & lose data- we have a Darwin Awards for Dead Data on meta at AD... a sad list. – Tetsujin Nov 21 '17 at 19:52
  • Indeed, it is a valid point. I've been on the other side of the table, having to work with people who either dont want to spend much money or they did the previous mistake and it is me who has to repair it by hand, thats why I allways try to find the non-conventional way. I've screwed many disks, but I only lost information once because dd didn't copy the disk properly but didnt throw a warning. Since then I allways check manually if backups are done correctly and never made a client lose a single bit. Btw: removed the downvote and gave you a +1, considering possible mistakes from future users – DGoiko Nov 21 '17 at 19:57
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With a few clarifications and extra steps, the instructions here worked for me for a 2019 MacBook Pro 13-inch.

I was able to reallocate a 1TB HD from 100GB MacOS/900GB Windows to a more sane 750GB MacOS/250GB Windows. I did not need to reinstall either OS.

There are three main steps here: Resize the Windows BootCamp disk, Create a new partition from the unallocated space, Merge the new partition with your MacOS partition.

IMPORTANT - Be sure you have a backup of the Window partition (and, for safety, the MacOS partition also). I didn't end up needing them, but you might get unlucky and I don't want you to be sad.

Resize the Windows BootCamp disk

  • Boot to Windows partition.
  • Install MiniTool Partition Wizard (free).
    • Beware - it will try to install AVG Free. It didn't seem to give an option to not install it, and I had to delete it later.
  • Launch MiniTool and load the Partition Manager.
  • Find the Bootcamp partition that is too large.
  • Right-click, and choose "Move/Resize".
  • Resize the partition down to the size you want.
    • IMPORTANT - Be sure the empty space occurs at the beginning of the partition (drag the arrow on the left -- not the arrow on the right). If you place the new partition at the end, you won't be able to use the freed space to expand the MacOS partition later.
  • Click Save to return to the main screen, the click Apply at the top left corner.
  • A box will pop up telling you that you need to reboot to apply the changes. Reboot to apply the changes.
    • IMPORTANT - Be sure to reboot into Windows again.
  • MiniTool will apply the changes. It might reboot again - be sure to go back into Windows.

Create a new partition from the unallocated space

  • Boot into Windows partition (if not already there).
  • Open MiniTool once again and go to the Partition Manager.
  • Your new unallocated space should appear before the BootCamp partition.
  • Select the new unallocated space, right-click, and choose Create to create a new partition.
    • I don't think it matters what kind of partition you create, so long as it is one that MacOS can reason about -- I chose FAT32.
    • If you don't create a partition here, MacOS doesn't seem to be able to find the unallocated space.
  • Save and Apply the changes again. A reboot shouldn't be required.
  • Reboot into MacOS.

Merge the new partition with your MacOS partition (adapted from here)

  • Boot into MacOS partition (if not already there).
  • Open Disk Utility. You should see the new partition just after the container holding your main Macintosh HD (but still within your disk).
  • Click the disk and choose "Partition" (you may need to choose "Partition" instead of "Create ADFS").
  • Select the new volume you just created (the one that should be merged into the existing MacOS volume).
  • Click the "-" button below the pie chart.
  • Apply/save.
  • This will expand the MacOS partition to include the newly created partition.

Your MacOS disk should now be larger.

NOTE: I am not affiliated with MiniTool in any way -- the tool just ended up working for me. There may be others that will do the job as well.

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You have to use a partition utility like GParted.

If you are using APFS as filesystem GParted cannot modify it. You'll have to find a tool able to do so, and do the resize in parts, first the physycal APFS partition and then the Windows NTFS. If there's no software which automatically does it it involves a VERY HIGH RISK of data loss. Keep this in mind and backup your data (or whole disk) before.

If you want to try the "easy way" first follow this guide about resizing bootcamp using minitool partition wizard. It will only work properly if the NTFS partition of the Windows installation is a proper NTFS partition. Keep in mind that BEFORE doing this you'll have to shrink your mac partition using mac's Disk Utility. It will not allow you to make the bootcamp bigger, but it will make room for you to enlarge it with MiniTool (or any other tool capable of working NTFS under the partition layout your HDD has). The full procedure is explained here:

Yesterday expanded my bootcamp partition from 50 up to 100 Gb using Mini Tool Partition Wizard Home Edition, a Freeware Windows Program after seeing this video: http://www.youtube.com/watch?v=WeKeawqxUa0

Note that I have OSX Mavericks, Steps are:

1) backup all your files (optional but strongly reccomended).
2) Using OSX Disk Utility resize MacintoshHD partition leaving unallocated space as much as you need to add to bootcamp partition.
3) Set Bootcamp as Boot Disk and restart the mac.
4) in Bootcamp with Windows running launch Mini Tool Partition and select the bootcamp partition.
5) Choose "expand" option in order to expand the partition using all the unallocated space.
6) The program prompt to you to restart the mac for apply the task, cause is not possible while the partition is mounted and windows running.
7) Restart the mac and then automatically Mini Tool Partition will do the job in a "graphic msdos like" form.

Now the long way around:

First of all, before doing anything MAKE A BACKUP OF YOUR HARD DISK. For zero risks use dd (diskdupe) to backup every single bit of the harddisk into a disk image. You can check how to do so here. If you dont want to risk to reinstall everything from scratch make sure your backup contains the partition table and the partitions, or that you are totally able to restore that backup, even if you bought a new hard disk. This is a critical step if you're not confortable with partition modification (its recomended even if you are). Whenever you touch a partition you are risking your data, and even though most times there will be a way to recover your info even if you screw it up without a backup, there are chances you'll overwrite important data and loose it forever. The risk depends on the operation performed and resizing is a particularly risky operation!. If you are curious about what partitioning is about, you can check this beginner explanation to get some insights of what you are actually doing.

Then you have three chances:

  • Install a partition edition software on your Mac. I'm not a mac user, so I can only give you one example, Disk Utility, which I believe it is included in mac distros. You can check this discussion to find more examples. All I could find on google was comercial software, but as I said, I'm not a mac expert, so there may be a GParted port around or something like that.
  • Boot using a liveCD/USB like SystemRescueCD or GParted Live and use GParted which is installed in the live distribution. There are many CDs to do this, like Partition Wizard, Partition Manager, Partition Magic, etc. In order to use thid method you will check how to boot using a CD on mac, which is a different topic.
  • Do it from your Windows OS instead from MAC following a Windows tutorial. There are plenty around, like this one.

Personally I allways use liveCDs to modify partitions, as they are much safer. Why is this? Because if you resize a partition you are using (from whithin the native OS) your system has to reboot and enter in some short of "special boot envinronment" (its not that, but just to simplify) and resize the disks from there. Those aditional steps add many failure points to an operation which is enough risky by itself. If you can, allways resize OS partitions from liveCDs.

And remember, make backups! This is a critical step, and deserves to be repeated over and over my post. MAKE BACKUPS!

Also, a link about resizing APFS. I'm sure you can shrink (or increase) the virtual windows partition first and then the actual partition. I don't know if the guy who said it is impossible took all his knoweldge from youtube tutorials or he's an actual computer engineer, but as a compute engineer i'm telling you there's no such thing as impossible, specially if apple provides a tool to resize. However, take into consideration what he said and DO A BACKUP!

More questions about APFS resizing here

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  • Like DGoiko mentioned, make backups of your important data, installers, and settings to an external HD. Separate backups for each environment. It's easy to make a mistake with disk resizing tools. Also, make sure you have a lot of room to spare on the disk. This is a good opportunity to back up externally and move files externally which you don't need every week. – Christopher Hostage Nov 20 '17 at 21:10
  • Don’t ever touch the partitioning from Windows! There are only 2 apps that won’t simply break Boot Camp completely, Paragon Hard Disk Manager & TwoCanoes WinClone. afaik, neither can yet handle APFS. – Tetsujin Nov 21 '17 at 8:00
  • @tetsujin you are sooooooo terribly wrong xD – DGoiko Nov 21 '17 at 14:31
  • Would you care to elucidate, or is the ‘o’ on your keyboard stuck? – Tetsujin Nov 21 '17 at 15:53
  • @tetsujin This is for older versions: discussions.apple.com/message/24377993#24377993 This uses disk utility and then partition magic,but could be gparted from boot disk.This guy does it in the wrong way using partitiion manager from windows. They changed the filesystem, but there has to be some tool to handle it, for sure, and if not, he can allways drop the info to a new FS. If you are right (which i highly doubt) and there's no tool to do it in a single step with the new FS you could enlarge the APFS and THEN the virtual partition underlying. – DGoiko Nov 21 '17 at 19:19

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