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I use a 1 TB external drive for my Time Machine backups. Get Info on the drive shows that I have 807 GB available. But if I do a Get Info on 3 of the backups, the total of the 3 folders is 321 GB, and there are many more folders on this drive. So how can there be 807GB available, when only 3 folders are using 321 GB? Should I be concerned, or is this just some type of anomaly?
MacBook Pro 13″, macOS 10.14
Time Machine uses hard links to unchanged files. To apps that operate above the level of the disk controller cannot tell the difference between a hard link (a reference to a storage location on the disk) and the actual file to which the reference points. So, when it calculates the folder size, it calculates the size of each of the actual files, not the references to those files.
So, imagine if you never changed or added anything to your drive since the first backup. If that backup was 321 GB of actual files, every monthly backup folder would contain what looks like 321 GB of files, but they really contain almost nothing, just the minuscule overhead of the hard links.
Time Machine uses hard links to unchanged files. To apps that operate above the level of the disk controller cannot tell the difference between a hard link (a reference to a storage location on the disk) and the actual file to which the reference points. So, when it calculates the folder size, it calculates the size of each of the actual files, not the references to those files.
So, imagine if you never changed or added anything to your drive since the first backup. If that backup was 321 GB of actual files, every monthly backup folder would contain what looks like 321 GB of files, but they really contain almost nothing, just the minuscule overhead of the hard links.
I don't think you can trust Folder sizes in TM, it deals with a dizzying array of Aliases.
Thank you, Barney. That makes sense.
Thank you. That's reassuring.
Time Machine folder sizes
