![]() The top-level volume contains essentially the same folders as you’ll find on an older single-volume layout, but drill down through the System folder to Volumes, and you’ll find another Macintosh HD which has a different set of folders. Viewed in the Finder, with hidden items revealed, there now appear to be two volumes both named Macintosh HD. However, to preserve the illusion of simplicity in the Finder, and to link the new System and Data volumes together, requires more smoke and mirrors, making the structures quite different. The change made to this structure in Catalina might appear simple: in a bootable APFS container, there is a fifth volume. This is quite different from HFS+, where the volume isn’t within a container, making the first HFS+ volume on disk4 the much simpler disk4s2, as disk4s1 is the EFI partition. Unix names for those volumes are a bit more complicated, as the APFS container is considered to be a ‘synthetic’ disk, so is labelled disk1, and the four volumes within that then become disk1s1 to disk1s4. Its total volume count for that container is 4. Select a bootable container, though, and it reveals the VM volume, and the fact that two volumes aren’t mounted. Of all the volumes and containers, the Finder normally only shows those coloured blue, even when you reveal hidden items.ĭisk Utility goes a little bit further, but still only lists the visible volumes at the left. The other three volumes – one containing code to be loaded early when starting up, another storing ‘virtual memory’ working files, and the Recovery volume – are either unmounted during normal running or hidden. This is shown in the second example, disk2, in the diagram above, and disk4 is its equivalent in HFS+.īootable APFS disks, as shown in disk0 at the top, have the same top level structure, but within their APFS container are four volumes, of which we’re normally only shown disk1s1, commonly named Macintosh HD. However, APFS volumes within the same container grow and shrink in size as they need, as they all share space within that container.Ī simple external disk used for storage and in APFS format therefore has one APFS container, within which there is a single APFS volume. This is because containers behave like HFS+ volumes, with fixed size and unable to share free disk space. ![]() Here’s one important difference between HFS+ and APFS: APFS doesn’t put its volumes at the top level within the storage structure, but inside a container. Each disk contains a hidden EFI partition, together with HFS+ volumes and APFS containers as created. There are two invaluable commands which reveal disk and volume structures in their full detail: the older diskutil list, and a new supplementary diskutil apfs list which concerns itself with APFS volumes.ĭisks, internal or external, commonly come in two forms: those using the old HFS+ (Mac Extended) file system, which are still required for local Time Machine backups, and those using the new APFS.
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