Many issues are concerned with insufficient storage for Time Machine's disk. Mine is the opposite, it would seem that available storage is ignored.

  • MacBook Pro: 15-inch 2018
  • Memory: 16GB 2400MHz DDR4
  • MacOS Big Sur Version 11.1
  • Time Machine disk: Seagate Backup Plus Drive, 8TB
  • Time Machine works correctly. I can explore material back to 2016.
  • Encryption: I started it this week. It's at 18%. I recognize that it's a slow process.
  • Automatic backup is turned off in order not to delay encryption.

Yes; backup not an archive -- but I like sometimes to be able to explore ancient material.

Using info last night I saw 940,570,304,512 bytes used; call it 940,570 MB. I did a (manual) backup. The amount used diminished to 939,733 MB. A succession of further checks showed 939,800 ... 939,816 ... 939,818 ... so increasing ... 939,906 ... 939,908 MB. I shut the machine down. This morning, upon start-up, that figure is reduced; it's now 939,760.

It's as if a limit of 1TB is somehow set -- yet I have an 8TB drive.

  1. Has such a limit been set somewhere?
  2. If so, where?
  3. How can I see it?
  4. How can I reset it?

1 Answer 1


Time Machine compresses backups based on a regular schedule. Ultimately you will end up with weekly backups. This occurs regardless of your free storage space.

When you run out of space, it will start deleting whatever backups you have, oldest first, until you have enough space to complete a new one.

  • With encryption in progress, the system shows, say, 'Encrypting Backup Disk... 36%'. Does that mean that some backup-entries are encrypted, one by one, working backward from the latest, and 36% or them are done, of is it 36% of estimated total storage-space for the backup? It seems to suggest that 36% cannot be viewed by hackers but the remainder is still vulnerable. Does that actually follow?
    – Algol60
    Jan 13, 2021 at 3:37
  • The percentage should be going up – and it refers to the space on the disk as a whole that has been encrypted. It's not backup-specific since it's handled by APFS itself.
    – Ezekiel
    Jan 13, 2021 at 13:27

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .