Boot Camp Assistant is not able to use ISO where install.wim>4 GB

Number:rdar://44874032 Date Originated:September 28 2018
Status:Open Resolved:
Product:Disk Product Version:
Classification: Reproducible:
Disk Utility

When installing Windows via Boot Camp assistant, if the ISO has an install.wim > 4 GB, the installation fails when running Boot Camp assistant.

Steps to Reproduce:
1. Get yourself a Mac
2. Download a recent Windows ISO from Microsoft that contains multiple editions like "en_windows_10_business_editions_version_1803_updated_march_2018_x64_dvd_12063333"
3. Run Boot Camp Assistant, and select that ISO.

Expected Results:
BCA will crunch for a while then present the partitioning screen, and after that reboot and start installing Windows.

Actual Results:
There is an error about copying files.  There are 2 partitions that are created (one for installing Windows on to, and one that the files are copied on to). The format of the installer partition is FAT32, which only handles files up to 4GB. If I try to manually copy the files from the ISO to the install partition, the copy fails due to the 4.35GB Install.wim file in Sources. If I re-format the install volume as exfat, the files will copy successfully. Also, if I format the BOOTCAMP volume as NTFS and reboot to the install volume, the install succeeds.

10.14 (389a)


Please note: Reports posted here will not necessarily be seen by Apple. All problems should be submitted at before they are posted here. Please only post information for Radars that you have filed yourself, and please do not include Apple confidential information in your posts. Thank you!