So, my situation is (still) that post-High Sierra upgrade, I ended up with three APFS containers, with one volume each. There's still (as of 10.13.4 beta) no way to merge containers, but I've found there is a way to pull in a volume from one container to another, given enough space: the Restore button in Disk Utility, with the special Restore to new volume checkbox. Cool! Except it doesn't work It gets busy for a while, and then near what appears to be the finish line, it fails to "invert the target volume", whatever that means. So, what is "inverting target volume"? what are the equivalent commands in diskutil/asr/etc. so I can try this step-by-step in Terminal? what resource is busy? Surely it's only talking about the volumes within the same container, but those are all unmounted.