rallycar27 wrote:
Interesting articles! Any insight on these further questions?
1) Is there a way to find out the size of these snapshots without deleting or trimming them? I don't desperately need this space to become available for something immediately and don't want to monkey with something that's currently working fine, but would love to know if they are indeed taking up the entire 382 GB of purgeable disk space.
I'm not aware of anyway to tell the size of the snapshot because the snapshot isn't a separate file or folder, but the file system itself. Unless you had some very large files/folders when the snapshot was made and you later deleted those large files/folders, then the snapshot will still retain a copy of those large items until the snapshot is deleted. I'm not really familiar with the APFS snapshots beyond the links I shared, but according to what I've read most snapshots are deleted in about a week, although TM snapshot backups may not if you haven't connected your TM drive in a while.
I can tell you from using the Linux BTRFS file system which also has file system snapshots, that if you have a lot of snapshots, then the space consumed on the drive can decrease rapidly because the file system needs to keep track of the various changes for every file/folder within each snapshot. I assume the same is true with APFS.
2) Will macOS automatically delete these snapshots/purgeable data when I need it for something else? If it will, that's great and I'll just stop worrying about it! The first article was a little unclear on this, saying "But if each snapshot could rise to 1 TB, and you’ve got dozens of snapshots, they could rapidly come to occupy all the free disk space, and block the file system from functioning." So it's unclear to me how common it is for a user to find themselves in a situation where they are putting commands into Terminal to trim or delete snapshots.
In theory the APFS snapshots should all be handled by macOS and will be deleted within a week in most circumstances except maybe if you haven't connected your TM backup drive in a while. Once TM transfers the contents contained within the snapshots, those snapshots should be automatically deleted by macOS. Unless you have absolute no free space left on the drive I don't think any user should concern themselves with the snapshots.
3) Whoa, I just opened Time Machine without my external HDD plugged in and sure enough there were some backups there. I had no idea!
4) Why aren’t time machine snapshots a category in the About>Storage area if they’re taking up so much internal storage space? Because it’s purgeable and will automatically delete if necessary? It sounds like from those articles it doesn’t always purge correctly and needs to be manually deleted under certain circumstances, which is confounding to me because I want my backups to be stored on an external hard drive, not locally in these “snapshots” stealing space on my internal SSD. I kind of wish there was a setting in System Preferences that could disable this local storage of snapshots. Even if I probably were to leave it enabled, it would bring users' attention to the fact that it's even happening, which would be helpful alongside showing it in the About>Storage graph. Apple could make this a little clearer. I freaked out when I first saw that Disk Utility was showing that I only had 256 GB free! But now I understand the information they are trying to convey. I just think it could be a little clearer.
APFS snapshots are only intended to be an internal macOS process hidden from the normal user. There is no reason to have any specific information about APFS snapshots in the GUI for most users.
Purgeable space could include other things besides AFPS snapshots.
The local snapshots are just TM preparing a backup and those local snapshots are not meant to be the permanent location of the backup. The local snapshots are just temporary until you connect your TM drive so the snapshot (or perhaps just the changed items within the snapshot) can be transferred to the external TM drive. Other APFS snapshots may be temporary "restore" points created by macOS during OS updates and again should be automatically deleted after a set period of time.
I would only check the free available storage using the Finder and "Get Info" on the drive volume or on a folder. Unfortunately Apple's storage management assessment found in various Apple apps does not always correctly show the correct values for the various storage categories.
