Catalina Time Machine: Past explanation for "Out of Space" is incomplete

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Level 1

4 points

Catalina Time Machine: Past explanation for "Out of Space" is incomplete

The discussion of "Out of Space" in a previous question states "Once Time Machine finds it cannot free up enough space for a new backup it reports the disk is full. You can either erase the backup drive and start over or get a larger drive." This fails to get at the problem: What's wrong with the design of Time Machine that it can't reliably keep discarding the oldest incremental file? Relatively few files actually change over time--it shouldn't take much space to track that.

I have a TM drive that is 3 times the size of my system drive. If TM were working properly, it should just hum on forever. But instead, I keep getting the message Backup Failed, Out of Space. With 453 Gb free, how is it possible that TM can't do an incremental backup?

BTW, I've had a continuing problem since Sierra: "Entering TM" produces a black screen, without the stacked windows. I'm able to get the standard TM screen to appear for only a second as I close this. What's up?

Posted on Jul 23, 2021 7:53 AM

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Answer 1

PRP_53

Level 10

91,807 points

Jul 23, 2021 8:41 AM in response to Techie242

Have seen other people with similar issues as yours. In their cases, the issue was not the Time Machine Drive itself but rather in the Internal Drive from which the snap shots are stored before being moved to the TM Backup Drive.

Worth reading from the Developers Site on that aspect of TM and Internal Drive

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Answer 2

Techie242 Author

Level 1

4 points

Jul 23, 2021 8:53 AM in response to PRP_53

Are you suggesting that the error message is actually misleading? (There's plenty of space on my internal drive, BTW.)

I remember reading a three-part series on the very complicated processing of TM. of course, I don't remember the details... ;-)

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Answer 3

PRP_53

Level 10

91,807 points

Jul 23, 2021 11:28 AM in response to Techie242

Well, since the internal drive has a lot of empty space and the external also has a lot of empty space- can you put the drive with the issue aside for now. Then introduce a new TM Drive and set it up as the default drive and test is the original issue replicates itself. More of a test than anything else.

No chance any Cleaner or Optimizer applications have been run or installed ?

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Answer 4

Techie242 Author

Level 1

4 points

Jul 23, 2021 12:17 PM in response to PRP_53

I've looked more closely at the error details. I now see that TM is attempting a full backup, and that's why there isn't space. The question is why??? It should just merrily go along doing incrementals, shouldn't it? Doesn't that go against the entire design scheme of TM?

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Answer 5

Techie242 Author

Level 1

4 points

Jul 23, 2021 1:55 PM in response to PRP_53

Thank you for that suggestion. I ran DU. The volume wouldn't unmount, so repair wasn't possible. I suspect that's because it is running under SoftRAID as a mirror. I tried my other mirror volumes, and got the same "Can't unmount" message.

I'm curious why TM would decide it needs a full backup...

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