At that time, the latter included two blocks of data, ChangedDoc1 (red) and ChangedDoc2 (blue). That contains the file system metadata (red), which includes the two folders (pale yellow) and references the data for two files: OldDoc (blue) and ChangedDoc. In this example, a snapshot was made a little time ago. To understand what’s required to copy a snapshot within a Time Machine backup to APFS, or anywhere else for that matter, I’ll consider a simple scenario. It’s also essential to remember that HFS+ backups can only be copied to another HFS+ file system, whether on a physical or virtual disk, as without support for directory hard links, the whole scheme fails. Thus copying an HFS+ backup to another HFS+ disk is just a matter of patience, and hoping that there are no errors in amongst all those millions of file system records. Although a slow and time-consuming task, making an exact replica of the original is straightforward. Those backups consist of a single file system containing millions of files, folders, and both file and directory hard links. Prior to Big Sur, all Time Machine backups were made to volumes (or images) in HFS+ format. To see what the problem is, we need to go back and consider what it means to make a copy of the two different types of backup used by Time Machine. Look in the documentation for command tools like diskutil and asr, and there’s no mention of imaging, copying or restoring snapshots within an APFS volume. Look in the master cloning utility, Carbon Copy Cloner, and you’ll be politely informed that copying to or from an APFS Time Machine backup volume isn’t supported. What had been a minor and essentially silent problem suddenly became more significant: how can you make a copy of your new Time Machine backup on an APFS volume, then? The answer, as far as I can see, is that you can’t. Big Sur changes this with the introduction of Time Machine backing up to APFS volumes, which uses snapshots to store those backups. Few apps other than Time Machine made much use of snapshots, and in Time Machine they were only made on APFS volumes being backed up, and were automatically removed after 24 hours anyway. Until Big Sur, this didn’t make a great deal of difference. Try making a clone of an APFS volume now and you may not even notice what’s missing from the copy: snapshots.
Sadly, since the introduction of APFS in High Sierra, that has now stopped working for those volumes formatted using the new file system.
Carbon copy cloner apfs mac#
One day we’ll look back and remember fondly when it was possible to clone any Mac volume to an identical copy.