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I have an external HDD with several APFS volumes containing all my files. I want to preserve a copy of the files at a given time, in case they get accidentally modified or deleted. Creating manual snapshots of the external HDD volumes on that very same external HDD seems like a perfect solution.

However, I was not able to find a way to create APFS snapshots using macOS system utilities:

  • Disk Utility GUI reveals snapshots and it's possible to mount or delete already-existing snapshots but there does not seem to be a way to create new ones
  • I would expect diskutil to be able to do that but according to its manual diskutil afps snapshot can only be used to list, delete and mount snapshots but there does not seem to be a way to create a new snapshot
  • I was able to create local snapshots of a system/boot SSD with tmutil snapshot but (1) these are then managed in a similar manner to snapshots created by the Time Machine so will eventually be deleted as stated by the command output: NOTE: local snapshots are considered purgeable and may be removed at any time by deleted(8). and (2) there does not seem to be a way to create a snapshot of an external drive with that command. I tried to use tmutil snapshot /Volumes/MyExternalHDDVolume (following the syntax used by tmutil listlocalsnapshots) but that simply creates a snapshot of my internal SSD.

According to online sources, 3rd-party tools like Carbon Copy Cloner are able to create local snapshots, but I am not sure how reliable those snapshots are (considering no official filesystem documentation is available) and whether Time Machine would delete them at some point.

Is there any way to create manual snapshots of an external drive APFS volume with built-in system tools, whether GUI or command line? In a perfect world, these snapshots would not be in any way touched by Time Machine (i.e. they would not be deleted), but assuming Time Machine would only delete manual snapshots when space on the disk runs out it would not be a big issue (considering there is plenty of disk space available on that external HDD).

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  • In first paragraph you are looking for a 'perfect' solution. What you are suggesting (even if possible) is an imperfect solution. A nearer perfect solution: Get a large HDD to use as a TM (or CCC) destination to backup all your existing APFS volumes. That protects against hardware failures as well as your mistakes.
    – Gilby
    Dec 3, 2022 at 22:08
  • @Gilby Thank you for the suggestion but I already have copies of my files on different devices with different file systems (all files on ext4 and NTFS drive and most important ones on more than one ZFS and ext4 drive) so I am protected against hardware failure. The very purpose of that large HDD where I have another copy of all files and where I want to make snapshots was to create a "versioned" copy of all my files until I run out of space.
    – Rafal
    Dec 4, 2022 at 1:36
  • @Gilby Considering I am already using this large HDD to store my files, unless I misunderstood your suggestion I would have to either buy another drive or use Time Machine to backup the existing volumes to another volume on that same drive (where TM backup of my laptop is already stored) if that's possible at all. Unfortunately, in the latter case, the space-saving benefits of snapshots (or APFS in general) won't be realized as duplicated data on different volumes can't use the same storage blocks the same way snapshots and copied data on the same volume can.
    – Rafal
    Dec 4, 2022 at 1:40

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