I was one of the unfortunate souls to have purchased a 2013 27" iMac with a 3TB Fusion drive thinking it would be able to avoid the Apple obsolete list until at least 2020, and of course, be able to run Windows10 for the few Windows-only programs I use for work that don't have Mac counterparts. I was right, up until Mojave. When I tried to install Mojave the first time, I was alerted that I would have to remove my Bootcamp partition, and that I wouldn't be able to install Windows on this particular computer via Bootcamp after installing Mojave. So far, that's been the case. What I wanted to know was, Why? Luckily, I have a 2011 MBP that runs High Sierra and Windows10 (via Bootcamp) just fine, so work can still be completed. But my iMac is the go-to machine, and has the larger storage (3TB Fusion), so why wouldn't I want to run Bootcamp on it? Alas, when I attempted to run Bootcamp Assistant after installing Mojave, I was met with a message that Your disk could not be partitioned An error occurred while partitioning the disk. Please run Disk Utility to check and fix the error. So I did. On just the Macintosh HD volume, and then on the Fusion drive. Something that stood out was that when it got to the volume VM and verifying allocated space, there were about 50 lines of warning: Overallocation Detected on Tier2 device: (1125900443662074+1) bitmap address (1cd68) with subsequent changes in the addresses in parenthesis. It ended with: too many warnings generated; suppressing subsequent ones. Performing deferred repairs. The volume /dev/disk0s2 appears to be OK. Storage system check exit code is 0. Operation successful. Great! I'd try to run Bootcamp Assistant again, and would again be directed to run First Aid to check and fix errors. I did a little more reading, and thought I'd try deleting the 4 snapshots that originally appeared. So, I did. Then, I rebooted into single user mode and ran /sbin/fsck -fy to see if that would do anything. Not really. I'm stopping short of erasing everything and starting from scratch. Mojave seems to be running fine on the Mac side of things, and if overallocations are a bad thing, I can't tell from normal day-to-day use of MacOS. But, it sure would be nice to put Windows10 on this machine without having to go through Parallels or VMware. So, does anyone know how to fix Overallocations, or Underallocations, for that matter?