I have a mid-2015 MacBook Pro running High Sierra that I wanted to install Boot Camp onto, in order to run some Windows software. I'd designated 200Gb on my SSD for Windows.
Boot Camp Assistant kept failing with a "Not enough space on startup disk" error, and trying to remove the partitions.
I'd like to share my experience in the hopes that it will help others.
MacBook Pro 15″, OS X 10.10
(Possible red herring: I found an article that said this problem could be due to some parts of the Windows 10 ISO being over 4 Gb. I used a downloadable tool called Boot Camp ISO Converter to go through the ISO and break up any parts over 4Gb. https://twocanoes.com/using-larger-windows-10-isos-with-boot-camp-assistant/ It is no longer being supported and may not be necessary anyway--I just looked at the ISO (in Finder window, right-click and choose "Open"), and I don't find any individual files over 2.1 Gb.)
The problem seemed largely due to the size of the OSXRESERVED partition. It was defaulting to 8Gb. The Windows 10 ISO is 5.79Gb and it seemed not to have enough room to run the installer.
So I used Disk Utility in my Mac's Utilities folder, highlighted my disk, clicked the Partition icon, clicked the Partition button, selected the OSXRESERVED partition, and clicked the "-" icon to remove it. Then removed the BOOTCAMP partition the same way. I clicked Apply to remove both and restore my disk to its previous state.
Then I specified my own OSXRESERVED and BOOTCAMP partitions as follows: first, 20 Gb FAT32 partition named OSXRESERVED. Then a 200 Gb (maybe overkill, but I had a lot of extra disk space) partition that I specified as APFS (gets converted to NTFS with the installer). Clicked Apply to create both.
I copied the ISO to the OSXRESERVED partition by opening it & dragging & dropping the pieces onto OSXRESERVED in the Finder.
Then I rebooted while holding down Alt to boot into Windows. I needed to specify my WiFi for some reason.
Once in Windows, I could double-click on Setup.exe to install it.
When I rebooted into my new Windows, my trackpad wouldn't scroll and I couldn't get online. Wifi kept failing with some error message that implied the drivers weren't set up.
I rebooted back into OS X and ran Boot Camp Assistant "Action -> Download Windows Support Software." Booted back into Windows, went into the OSXRESERVED sector (under "My Computer") and double-clicked on something like startup.exe in the Support folder--NOT the one in the main folder! That installed a set of drivers in Windows, and from then on, my trackpad worked, I could get online, and I could download and run my Windows software.
(Possible red herring: I found an article that said this problem could be due to some parts of the Windows 10 ISO being over 4 Gb. I used a downloadable tool called Boot Camp ISO Converter to go through the ISO and break up any parts over 4Gb. https://twocanoes.com/using-larger-windows-10-isos-with-boot-camp-assistant/ It is no longer being supported and may not be necessary anyway--I just looked at the ISO (in Finder window, right-click and choose "Open"), and I don't find any individual files over 2.1 Gb.)
The problem seemed largely due to the size of the OSXRESERVED partition. It was defaulting to 8Gb. The Windows 10 ISO is 5.79Gb and it seemed not to have enough room to run the installer.
So I used Disk Utility in my Mac's Utilities folder, highlighted my disk, clicked the Partition icon, clicked the Partition button, selected the OSXRESERVED partition, and clicked the "-" icon to remove it. Then removed the BOOTCAMP partition the same way. I clicked Apply to remove both and restore my disk to its previous state.
Then I specified my own OSXRESERVED and BOOTCAMP partitions as follows: first, 20 Gb FAT32 partition named OSXRESERVED. Then a 200 Gb (maybe overkill, but I had a lot of extra disk space) partition that I specified as APFS (gets converted to NTFS with the installer). Clicked Apply to create both.
I copied the ISO to the OSXRESERVED partition by opening it & dragging & dropping the pieces onto OSXRESERVED in the Finder.
Then I rebooted while holding down Alt to boot into Windows. I needed to specify my WiFi for some reason.
Once in Windows, I could double-click on Setup.exe to install it.
When I rebooted into my new Windows, my trackpad wouldn't scroll and I couldn't get online. Wifi kept failing with some error message that implied the drivers weren't set up.
I rebooted back into OS X and ran Boot Camp Assistant "Action -> Download Windows Support Software." Booted back into Windows, went into the OSXRESERVED sector (under "My Computer") and double-clicked on something like startup.exe in the Support folder--NOT the one in the main folder! That installed a set of drivers in Windows, and from then on, my trackpad worked, I could get online, and I could download and run my Windows software.
W10 1903 and newer ISOs have a install.wim which is larger than 4GB and does not fit on a FAT32 USB or a FAT32 OSXRESERVED. This problem was corrected in macOS Mojave and later with an updated BC Assistant. If you use an older W10 ISO, you should be fine on macOS Sierra..
Boot Camp Assistant error: "Not enough space on startup disk" - SOLVED
