Resolved Discrepancy in available HD space

[Just_Kevin]

I expect this to be a basic question, which is why I have it in Mac Basics. I'm still getting accustomed to MacOS.

I noticed earlier today Disk Utility was reporting ~135GB of free space on my MacBook with a 1TB HD. I have since removed what I expect to be well over 100GB, I was not really keeping track. This was accomplished mostly by offloading larger and older folders/files to an external drive. I also realized I had double-digit GB in the Trash, mostly from video editing projects, which I emptied.

Disk Utility is now reporting less free space (120GB), it even dropped a few GB after a reboot. Settings however, is reporting nearly 600GB free space. I had not checked Settings prior to now.

From some research, this seems to be tied to Time Machine backups? The OS is keeping those files in case I need them back, but they would get deleted if were to need the space. This is why Disk Utility is showing ~120GB free, but Settings is showing the nearly 600GB. I have Time Machine pointing to an external SSD, but the OS is still keeping those files locally as well. I think they are only kept ~24 hours though?

That's my theory at least. Am I correct?

 

[Bigwaff]

There is option in Disk Utility to show APFS snapshots. You can delete them if you wish, or let macOS do it when it decides to reclaim the space.

 

[NoBoMac]

Disk Utility graph does not include purgeable space. Click the info icon at upper-right of the window which will return a window that shows "purgeable + free" (aka the value in System Settings) and individual lines for "free" (what's showing in DU screen shot) and "purgeable".

OS will handle purging purgeable for wear leveling purposes:

Get detailed information about a disk in Disk Utility on Mac

Use Disk Utility to see detailed information about a disk or volume on your Mac.

support.apple.com

“purgeable space”—space that macOS can free up when needed by removing files from your computer (you can’t manually remove the files that are designated purgeable, but macOS removes them as space is required)

 

[Just_Kevin]

Thanks for the responses. It's seems I was on the correct track with my thinking. Overall takeaway is to go by Settings > Storage to determine headroom available. I was a tad concerned based on how I know Windows OS works. When File Explorer shows low disk space, the OS starts behaving even more poorly.

Disk Utility is now showing nearly 350GB free. I also see the purgeable space in the Disk Info.

 

[Fishrrman]

I've never trusted nor relied upon the "storage" panel (shown on the right in the images you posted above) to provide useful info. I never look at it -- simple as that.

I don't use time machine at all, but I would suggest that you go to disk utility, set it up so that you can see the snapshots, and delete all but the most current one.

Of course, you'll have to remember to do this periodically, because they'll "build right back up" again over time (I think that's what happens, as I said, I don't use tm)...

 

[MacCheetah3]

What @Bigwaff and @NoBoMac said.

What is purgeable disk space?

When the Finder works out how much space is available on disk, what does it count as being “purgeable”? The answer may surprise you.

eclecticlight.co

Explainer: Snapshots

A great advance in APFS which enables Big Sur’s Sealed System Volume, and backups being made to APFS. Here they’re fully explained.

eclecticlight.co

View APFS snapshots in Disk Utility on Mac

In Disk Utility on Mac, view a list of APFS snapshots, copy information about the snapshots, and delete them.

support.apple.com

 

[NoBoMac]

Settings > Storage to determine headroom available.

Or can simply do a "Get Info" on "Macintosh HD" on the desktop. That will show free space and how much of it is in the purgeable category.

 

[benwiggy]

I was a tad concerned based on how I know Windows OS works. When File Explorer shows low disk space, the OS starts behaving even more poorly.

If you fill the disk with actual data, then yes, performance will be poor, but macOS can do its own housekeeping for the other stuff on the disk. This isn't Windows.