Finder says system drive almost full, but folders don't add up

[Ubele]

I have two Macs -- a late 2012 Mac mini and a 2015 13" MacBook Pro -- that I keep configured very similarly, with pretty much the same apps and data files. The mini has a 2.12 TB Fusion drive. Since the MBP came with only a 256 GB SSD, I boot from an external 1 TB SSD. Both have the latest version of macOS. I recently noticed that the MBP's system drive is almost full: both Finder and Disk Utility say that 998 GB out of 1.05 TB are used. My mini, on the other hand, says that 742 GB are used. So I added up the folder sizes on the MBP's drive, and they total 651 GB. That sounds correct, because the mini has some big Logic Pro projects that aren't on the MBP.

So where are the 347 GB of files on the MBP's drive that I can't account for? I did a Google search and found numerous threads on this topic, but very few are recent, and none of them seem to apply. I'm using a bootable clone to back up my MBP's external system drive, so it isn't a matter of Time Machine snapshots. The Library folder has only 77 GB of files (e.g., no huge Adobe cache files that's I'm aware of). The drive isn't partitioned. Any suggestions?

 

[Fishrrman]

Download DiskWave from here:
https://diskwave.barthe.ph
It's small in size and free.

Open DiskWave and go to the preferences.
Put a checkmark in "show invisible files".
Close preferences.

The DiskWave window shows you all your drives in plain English (no ridiculous graphical formats).
Click on any drive.
Now, you'll see what's ON the drive, listed in order of "largest to smallest".
You can easily locate what's eating up your space.

 

[Ubele]

Thanks, Fisherman. I ran DiskWave and selected "Show invisible files." The file totals added up to about 550 GB, which is less than the 651 GB when I added up the folder sizes in Finder.

However, a little more research told me to run About this Mac and click on the Storage tab. It revealed this:

All of that adds up to 998 GB. Clearly, I don't fully understand how macOS displays disk space used, because this doesn't match the totals in Finder. In Finder, it says that the System folder contains 9.88 GB of files. Here, it says 385 GB, which accounts for the extra used drive space. Is that even the same System folder, though? It's grayed out, so I can't see what files are in it. (On my Mac mini, there are 140 GB in the equivalent System folder).

I have my MBP's system drive cloned to a bootable 2 TB HDD using Carbon Copy Cloner. When I do Get Info on that drive, for Available space, it says, "923 GB (385.43 GB purgeable)." I assume that corresponds to the 385.61 GB in the system drive's System folder.

So, the question is, what constitutes those 385 GB of System files, do I need them all, how do do I know, and how do I delete what I don't need, if anything? I ran Optimize Storage from the Storage tab, and it didn't delete anything. I downloaded and ran CleanMyMac, and it found 48 GB of junk files, but it didn't delete them.

 

[ssmed]

Are you running a system that is storing snapshots for back-up - this can soon add up!

 

[Ubele]

Are you running a system that is storing snapshots for back-up - this can soon add up!

Ssmed, you're brilliant! I checked my Carbon Copy Cloner preferences, and snapshots were enabled by default on the source drive. There were over 40 of them. I disabled the feature and deleted the snapshots, and now all is well.