Well, we have one Mac with just (I can’t believe I’m saying just), 256GB of SSD. This is not very much because the system and applications need about 60GB and then with iCloud Photo Library and other sundries, it is hard to stay below 120GB. The solution have been an external drive with a RAID1 mirrored disks of 3TB and moving all the photos and videos over there.
However, in making copies and movies, suddenly, disk space shrinks to 30GB. What is going on. Well if you don’t have Space Gremlin, you should get it. We found the problem in
/var/folders, this is apparently the replacement for
/tmp that MacOS introduced. It gets rid of the problem of hacks through foreign accounts putting files in there and each /var/folders has permissions changed to only be visible to a single user.
It’s a good security thing, but can you just
rm -rf /var/folders like the good old days with
/tmp, well that doesn’t see like the recommendation, instead reboot your machine and it should clear all the temporary files out safely. This did work for us!