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TimeMachine is not removing any old backups.

The disk itself is plenty big enough (1TB, backing up a 500GB main drive), and I have (multiple times) reformatted it to start TimeMachine afresh. After about a month, the TimeMachine disk is full. I last formatted the disk August 19th, and now (September 10th) the disk is full. I can see about 490 backup snapshots, give or take every hour.

The TimeMachine disk is an SSD, formatted Mac OS Extended & Encrypted.

What could be causing this and what else could I try to get TimeMachine to thin out backups as it used to?

rowatt
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  • https://apple.stackexchange.com/questions/309143/how-to-thin-your-local-time-machine-snapshots-on-macos-high-sierra – anki Sep 10 '20 at 17:52
  • @anki that refers to local snapshots, not snapshots on an external TimeMachine disk. I could manually delete snapshots on the disk, but TimeMachine should be doing this automatically. – rowatt Sep 10 '20 at 18:05
  • Time Machine usually 'sticks' if any single file is too large to fit the space left. VM files are primary candidate for that type of issue. – Tetsujin Sep 10 '20 at 18:38
  • @Tetsujin understood, but I don't see how this could be due to a single too big file. Even after only 2 days of backups, the hourly backups are not being thinned, and at that point I still have 100's of GB free on the TM disk. – rowatt Sep 10 '20 at 18:51
  • So it still has hourly files from more than 24h ago? [It will, of course, have hourlies from yesterday, until midnight tonight] What OS? High Sierra used to do things like this, Mojave is better; I don't have Catalina to test. The usual 'fix' for dodgy TM drives is Disk Warrior, though it unfortunately can't deal with APFS drives yet. – Tetsujin Sep 11 '20 at 07:05
  • @Tetsujin yes - it still has hourly files from weeks ago (all of them as far as I can tell)! How would Disk Warrior, or indeed any disk repair app, help? I have formatted the drive multiple times and started afresh, but always the same behaviour. I'm on Catalina - 10.15.6. Prior to Catalina everything worked fine, but it didn't start until a few months after I upgraded to Catalina. – rowatt Sep 14 '20 at 11:02
  • Over the years, Time Machine seems to have gained a greater & greater propensity for screwing up its own file system; from the earliest changes towards APFS at Sierra & increasing with local TM backups. I find DiskWarrior is usually capable of 'unscrewing' it - though to be perfectly honest, I no longer trust Time Machine for anything more than simple deleted file recovery. It is certainly no longer reliable for Migration or disaster recovery. [One Mac here is still on El Capitan - the only one that never has issues] See https://apple.stackexchange.com/q/392734/85275 – Tetsujin Sep 14 '20 at 11:13

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I gave up trying to fix this directly, but after upgrading to macOS 11, and using the same SSD freshly formatted with APFS - as now supported in macOS 11 - TimeMachine is back to working as it should, with hourly snapshots being cleared out after 24hrs.

I can't say if the upgrade cleared out something corrupted, or if macOS 11 can now deal with the issue I was having, but it did fix things.

rowatt
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