Bootcamp – Stuck on ‘Partitioning Disk…’

The following post (see hyperlink) was useful, especially the bit about how you have to create a New partition when you're in the Windows installer. My previous answer was downvoted and I deleted it, but this actually solved the issue for me. https://fgimian.github.io/blog/2016/03/12/installing-windows-10-on-a-mac-without-bootcamp/

The partition map as well as the diskutil & diskutil cs listings looks completely valid.

Explanation:

• disk0: SSD part of a Fusion disk
• disk1: HDD part of a Fusion disk
• disk2: OS X base system (a recovery system mounted from disk1s3 or "downloaded" from Apple via Internet Recovery Mode)
• disk3: CoreStorage volume on disk0s2 & disk1s2
• disk4 - disk16: RAM disks needed in either recovery mode for temporary files
• disk17: Windows installer thumb drive

To install Windows with Boot Camp Assistant some free disk space is needed. To accomplish this the Core Storage Volume Group (including some other CoreStorage items) have to be resized. This is done by resizing the Physical Volume (disk1s2) on the HDD part and the inferior Logical Volume).

Usually the Physical Volume of the HDD part has a size of ~3 TB on a 3.1 TB Fusion disk and ~1 TB on a 1.1 TB Fusion disk. After choosing an arbitrary size for the Windows partition in BCA the PV and the LV will be resized accordingly.

Comparing it with my 3.1 TB Fusion disk you have chosen to assign ~320 GB to your Windows partition.

This assignment failed and no Windows partition was created. If BCA would have been successful your disk1 would look like this:

/dev/disk1
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *3.0 TB     disk1
   1:                        EFI EFI                     209.7 MB   disk1s1
   2:          Apple_CoreStorage                         2.7 TB     disk1s2
   3:                 Apple_Boot Recovery HD             650.0 MB   disk1s3
   4:       Microsoft Basic Data BOOTCAMP                324.0 GB   disk1s4

A failing Windows installation with BCA on a Fusion disk (with a CoreStorage stack) usually requires to completely backup your data with a backup app (i.e Time Machine), to rebuild/repartition the Fusion disk and to restore your old OS X system or restore it from scratch. The errors in the partition map and the CS stack following a failed Windows installation are usually not recoverable with the repair feature of Disk Utility.