Time Machine doesn't do a full backup although using a newly formatted drive

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Level 1

8 points

Time Machine doesn't do a full backup although using a newly formatted drive

Dear community,

I'm using a newly formatted external drive of 1TB (AFPS), however, after adding that as a backup drive to Time Machine, the size of the initial backup is only around 20GB - although my system drive of 500GB is almost full. So it seems that Time Machine continues to do incremental backups although I changed the drive. How can I get Time Machine to do a full backup on that drive and THEN continue to do incremental backups?

I ran into this problem because of another that occurred directly before:

When trying to do a backup on my regulad backup drive (manually, as I always do), Time Machine tells me that there's not enough space on the drive.

I've been using Tima Machine forever and was under the impression that it would manage such issue on its own by deleting the oldest incremental backup to make way for the most recent one (or something), but I must have been wrong (?)

After freeing up at least 100GB by deleting older backups manually, it still claims there wasn't enough space (although my previous incremental backups are between 10 - 30GB)
Finally, after eraising ALL of the backup files, Finder says there's allegedly only about 500GB of free memory, despite the drive actually being 1TB, and although my trash bin is empty (?).
Thinking that something's wrong with the drive, I'm formatting it, which then displays as it should at 1TB of free memory -- however, now I'm having the problem I posted above, I can't get TM to do a full backup. Even though I renamed the drive so that TM must think it's a new one. What the heck?!?

Using MacbookPro M1, Sonoma 14.7

Thanks a lot in advance!

Volker

MacBook Pro 14″

Posted on Oct 9, 2025 3:52 AM

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Answer 1

Top-ranking reply

jeffreythefrog

Level 6

13,788 points

Oct 9, 2025 8:38 AM in response to volker171

before trying to use the new drive with TM, did you remove the old one from TM preferences? I'm not 100% sure, but I am thinking that could be your issue.

you also said "After freeing up at least 100GB by deleting older backups manually, it still claims there wasn't enough space". removing backups manually is an excellent way of totally borking your TM. if it was me, I would fully erase the new drive, then add it back to TM.

and finally, the message about lack of space for TM, did it happen to say not enough room for a "local snapshot"? that means there is not enough room on your local drive. before a backup moves to your TM drive, it needs to make a snapshot on your local drive BEFORE it gets sent to the TM drive.

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Answer 2

Oct 9, 2025 8:32 AM in response to volker171

When erasing files, macOS does not immediately mark the space as "free"; it is "available", which means it could be made free, but usually it is not freed as quickly as we users expect.

If you are erasing all the contents of the drive, anyway, then I'd recommend reformatting it.

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Answer 3

volker171 Author

Level 1

8 points

Oct 9, 2025 2:01 PM in response to jeffreythefrog

I did remove the old drive from TM preferences. I mean, I'm still using the same physical drive, but I did reformat and rename it, so I figured that TM would take if as a new drive. Tried doing another backup, and TM calls it the "only backup", but it's only about 93GB despite my system drive of 500GB being almost filled up. This cannot possibly be a full backup?

Curiously enough, while creating the backup, at one point in time the progress bar said something along the lines of having written around 28,5GB corresponding to 6%, which would mean that TM was actually about to copy the full content of my HD, but then cut is short, for some reason...?

Regarding me deleting backups manually... uh oh... it seems I missed the point of the error messages TM was giving me. So when it said "not enough space on drive" it was referring to my SYSTEM drive, not the BACKUP drive? It didn't occur to me that I would need a certain amount of free space on the system drive in order to create backups... that said, I think I've been doing TM backups all the time with my system drive almost full to the brim, and there was never a problem... I wonder why it suddenly became one.

So when TM told me to delete files in order to free up drive space, I took it that I should actually delete TM backup files... which I first thought was weird, but since it actively told me to... now I realize that it probably was referring to my system drive...?!

I don't remember any message being about local snapshots, though. I've been reading about that while researching my problem, but I don't recall any of my error messages referring to that.

So, I would be really grateful for any further suggestions as to how I might get Time Machine to do an initial full backup. Thanks again!!

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