Update: I have done quite a few remasterings lately, and the filesystem copy takes about 3-5 minutes for ca 16GB on my SSDs. So it is in no way a showstopper, but the main reason I think I will keep it even if I switch from aufs to overlayFS, is (perceived) robustness. When the persistent store is damaged, some files get lost during the copy process, but this may be fixed by reinstalling the packages the lost files belong to, or restoring them from backup. It may well happen the overlayFS merging procedure is as robust (or even better) in this respect, but that remains to be seen. I have also become very convinced that using FAT32 for system administration is a very bad idea whenever it is possible to avoid it. But for daily use, it is the opposite for me: I keep the volumes at