Hitting the Limits of APFS
APFS limits the number of volumes which can exist within each container. The absolute maximum is 100, which is hardly likely to be reached unless you’re doing very peculiar things. However, there’s a smaller limit which is more likely to come into play: in any given container, the maximum number of volumes is the size of that container divided by 512 MiB, rounded up to the nearest integer. So if your container is 1.1 GiB in size, the maximum number of volumes it can support is not 100, but only 3.
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This results in the anomalous situation that:
- the smallest container size is 8.4 MB when there’s only one container, but around 20 MB when there are two or more;
- the smallest volume size is 8.4 MB when there’s only one container and one volume, 20 MB when there are two or more containers, or about 300 MB when there are two or more volumes in the same container.
Whoa! That is good stuff that @Howard Oakley has sleuthed. I keep coming back to this site and his own for exactly this kind of technical nitty gritty. I am no expert, simply a dilettante, but I love these file system details. You should have seen how excited I was when I found out my old SimpleTV network DVR (RIP) used JFS for the drive! Never having experienced that file system, definitely a fun read figuring out how JFS functioned.
Reading about APFS is similarly enjoyable.