Disk full when backing up, but the disk is 1.5 times bigger than the source

Software
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1

I’ve been using Carbon Copy Cloner for years and as much as I love the app, sometimes it can be super confusing and the support team, even though they reply pretty fast and try to clarify things, seem to make it even more confusing.

The logic (to me, at least) is that if my source is 1TB and my destination (backup) is 1.5TB, I have 500GB extra. So even if for some reason there’s a need to use more space temporarily (similar to how apps seem to require extra space, more than the app itself, while being installed), we are talking about 500GB, not 5GB. I also have 13GB free on my source so it’s 513GB, yet when I backup, I get the message in CCC that my disk is full.

When I check the destination in Finder and I do the math of all the folders there, I get around 750GB of used space, so what’s taking the other 750GB?

Snapshots are turned off for the backup disk, the same for SafetyNet so I really can’t wrap my head around this issue. Can someone please clarify what could be happening and how to work around this? Thanks.

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2

Are you sure that there aren’t hidden files there?

3

Try the DaisyDisk app (recommended) or something similar to explore your drive and see what is there.

4

Also read this Explainer: Disk free space – The Eclectic Light Company

5

In addition to advice given above… if you have many large files that change, it says in the support article at CCC’s support website that CCC will sometimes get to copying new files over to the destination before actually deleting old files – this may push you over the storage limit. (Do note that this article was for CCC 5 though.)

https://bombich.com/kb/ccc5/ccc-reported-destination-full.-what-can-i-do-avoid

The newer article on CCC 6 (below) does not mention this but this is still perhaps worth checking.

https://bombich.com/kb/ccc6/ccc-reported-destination-full.-what-can-i-do-avoid

Also, empty the trash, and check that there are indeed no hidden folders or files on the destination volume. Make sure that the SafetyNet folder is indeed gone after being switched off in CCC. Maybe consider reformatting/wiping the destination drive using the Disk Utility to make sure that it is indeed empty.

6

Thanks for your replies.
I’m already in touch with the CCC support team and it seems that this isn’t a normal behavior and we are trying to figure out what’s happening.

It seems that APFS, as good as it is in general, can be tricky in certain situations and maybe this is the case now, because there’s no 1:1 relationship between source and destination.

I’ve been trying to delete some files that I think are no longer needed, the trash, etc, so let’s see if that helps…