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blufrog

macrumors 6502
Original poster
Hi,

I have a really strange issue with Time Machine. It is only ever doing full backups, even for the hourly backups. Thankfully I don't have much stuff on the system disk, so each backup is "only" 40 GB each, but it doesn't change the fact every backup is the entire disk!

As I understand it, the first backup should be the full 20/30/40 GB of system data, then the next backup should only be the differences, meaning they should be 1/2/3 GB in size (or whatever changed).

It is a new backup disk, backing up to an external drive connected to Thunderbolt. It is APFS formatted, and created through TM itself after initially formatting the disk for APFS, etc.

TM enabled all the stuff it requires, and seemed happy with the disk.

I then added a second APFS volume and use this for all the normal stuff you'd use a disk for. I consequently have one physical drive sat on the desk, and two disks mounted. One of them is the TM backup disk, with the associated icon.

As far as I can tell, TM should be working correctly. I do not want to lose my first backup, as this was of the relatively empty drive before I added all my stuff to it. It is some 12 GB smaller than the install now I have added programs and mail and stuff to the system.

I understand how TM works, and what each backup is (1 backup per day for every day, 1 hour backups for the last 24 hours). This part seems to be working as expected.

What I want to do is delete all backups except the first one, then get TM to backup the disk in its current state, so I do not lose the empty "original" backup of the system before all the stuff I added.

Am I correct in thinking I can delete the folders from TM in Finder and not break anything? I will delete everything after the first backup; there will not be any weird gaps.

Interestingly, Disk Utility permanently shows "loading" for APFS snapshots, which should show the backups TM did? I'm wondering if this is indicative of a problem? It has been sat for maybe 10 minutes.

Screenshot for clarity.
 

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After looking at this again, it appears to be an accounting problem in Finder! It seems there are symlinks within the backup structure, and Finder is counting them all the time as part of the folder size, but when looking at the disk in Disk Utility, it shows the entire volume is only occupying 78 GB of disk space, which would be impossible without symlinks of some kind being involved.
 
it appears to be an accounting problem in Finder! It seems there are symlinks within the backup structure
They are hardlinks, this is fundamentally how Time Machine works. I wouldn't call it a "problem" since it's not really reasonable to expect a file browser to account for hard linking when calculating folder sizes, it's an exponential problem. Other tools specifically designed to check disk usage or specifically Time Machine will be able to tell you how much each backup takes, or what's changed.
 
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Yes: this is exactly how it's supposed to work. It's not a problem. Each snapshot gives the impression of being full size, but "borrows" the unchanged files from the previous snapshot.

In my experience, attempts to meddle with Time Machine usually make things worse.
 
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I haven't touched it since determining it is using links and the real size is "only" 70 GB or so. I was bothered whether it was taking half the external drive space. This is a problem I face with my backups for my other Macs.
 
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