Recently I’ve been trying to install Windows on an OS X laptop by using Boot Camp. However, every time the Boot Camp Assistant would tell me that “some files could not be moved” during the creation of the Windows partition. The most commonly suggested solution is a total reinstall of OS X, which I was absolutely not willing to perform.

I read online that this problem could sometimes be solved by using iDefrag in “Compact” mode to manually move all your files to the front of the disk before using the Assistant. However, buying and running this £24 software had absolutely no effect on the problem.

Looking at iDefrag’s summary view, it seems like there was a single unmovable “alternate volume label” block right at the end of the drive which might account for the problem. Anyway, I never got to the bottom of this, since I found an alternate solution that worked: hold down Apple+S during startup to enter single user mode and then run these commands:

/sbin/fsck -fy
exit


This just repairs any filesystem errors on your disk. It looks like filesystem errors were the true culprits, not unmovable files, since running the Assistant after this let me create the partition with no problems - Windows is installing right now.