What is taking up all my Mac storage, and how do I track it down?

February 12, 2025 6:46 AM

I have a MacBook Pro (c. 2020) with a 500-GB SSD that is running out of hard drive space. In the "Storage" pane of System Settings, the bar chart at the top shows 432 GB used, including 226.5 GB of "System Data". But when I go to the "Macintosh HD" window in the Finder, tell it to show hidden folders, and tell it to calculate the sizes of all the folders (visible and hidden), it adds up to a little shy of 200 GB. Why is there such a discrepancy?

It would be great if I could free up some or all of the storage space taken up by this mystery "system data", but I can't even find where these files are to inspect them. There are no other partitions on the hard drive (that I can see, at least.)

posted by Johnny Assay to Computers & Internet (11 answers total)

Do you use Chrome? Take a look at this question, it might be applicable.
posted by under_petticoat_rule at 6:50 AM on February 12

Go into your home folder, show hidden folders, and look at the contents of your Library folder. (Yes, there's a local Library folder as well as the global one.) That's the first place I'd look.

There are also lots of utilities that will look at the space usage on your Macintosh hard drive and help you clean things out. I haven't used one in a long time, so I don't have a specific recommendation, but it's a whole category.
posted by Winnie the Proust at 7:02 AM on February 12

Best answer: Yeah, I prefer Daisy Disk, but mostly because I've had a license for years and years. There are free equivalents like Grand Perspective that do mostly the same thing.

The thing that's always sort of a surprise in ~/Library is several ancient iPhone/iPad backups are sitting in there, taking up a surprising amount of space. I'm never restoring my 3-year old phone backup, Apple, but it's also not particularly visible in the filesystem, either.
posted by Kyol at 7:19 AM on February 12 [4 favorites]

1. From Finder, click the Go menu and choose Computer then double click your hard drive (typically "Macintosh HD" but may have a different name)
2. From the View menu, choose As List (Command-2)
3. From the View menu, choose Show View Options (Command-J)
4. click the checkbox for "Calculate All Sizes". Wait a while
5. in the finder window, click the Size column to sort by Size.
6. Now you can browse around and see what's taking up space, with the largest items sorting to the top of the window.
7. Don't delete things w/o knowing whether it's safe
8. (Optional) when you are done, turn off "Calculate All Sizes" (this can slow things down a bit, especially on older computers).
posted by soylent00FF00 at 7:47 AM on February 12

If you have Time Machine turned on, you will also be losing space to temporary local snapshots. These will automatically be deleted when the space is needed, but it can still be concerning to see your disk filling up. Apple has a support article describing how to delete these. Here's some discussion on Reddit.

Another possibility is swap space for the virtual memory system. I don't know how MacOS accounts for this in disk usage, but I do recall in the past that I've been able to free up disk space simply by rebooting my Macintosh.
posted by Winnie the Proust at 8:56 AM on February 12

Best answer: Seconding Daisy Disk, extremely functional and beautifully designed. I don't know if it's a deliberate attempt to drive people to iCloud or simple neglect, but those iPhone/iPad backups have gotten huge and they don't even include the apps. I ended up symlinking the backup directory my external storage to free up space on the boot SSD.
posted by wnissen at 9:59 AM on February 12

Have you emptied the Trash lately?
posted by seanmpuckett at 12:54 PM on February 12

Response by poster: Good suggestions so far, but no real progress.

• I've run into Chrome-bloat before, it's not fun. Right now, though, there are only two versions I can see inside the package.
• soylent00FF00's instructions are exactly what I did to arrive at the contradiction that I mentioned above. When I do that, I see 116 GB in /Users, 35 GB in /Applications, and so forth. After revealing hidden folders via Command-Shift-., the whole thing only adds up to about 200 GB. But when I look at the System Preferences breakdown, it shows about 200 GB of things it can identify (OK, that tracks) and an additional 227 GB of "System Data". Hence my confusion.
• I have rummaged around in ~/Library and deleted some stuff that I no longer needed (Old Steam games that no longer run, a backup of my "Drafts" folder from Mail that was 5 GB somehow). But I would have assumed that since this was a subdirectory of my own home directory, it would have been included in /Users/ when I did the top-level inventory I mentioned above. Is it not?
• The Time Machine caches are an interesting prospect; I do use Time Machine. But I'm getting error messages saying "your disk is almost full", so either they're not being deleted when the space is needed, or the problem is something else.
• Have you emptied the Trash lately? ... Give me a little credit, please. :-)

I'll give DaisyDisk a shot and see if it sheds any light.
posted by Johnny Assay at 3:31 PM on February 12

Best answer: Success! At least partially.

DaisyDisk revealed that there was an unused user account that I had forgotten about. It appears to be a clone of my user account from around the time I bought this computer. I have a vague recollection of creating a clone of my user account for what Seemed Like Good Reasons At The Time around the time I bought this machine; and when I deleted the old account (or the clone), I must have thought to myself, "Let's keep the old account's home directory, just in case".

Fast-forward to five years later and I'm pulling my hair out trying to figure out what's eating up 100+GB of hard drive space; it was (mostly) this old account's home directory.

Note that to find out about this account and the amount of space it was taking, I needed the version of DaisyDisk that you can download from the developers' website, which has the capability to "Scan As Administrator". The version available from the App Store doesn't have this feature.
posted by Johnny Assay at 5:10 PM on February 12 [2 favorites]

I see the question has been answered, and the problem solved, but wanted to leave a note that I use Disk Inventory X for this, which is free and makes it easy to find large files/folders. The Windows equivalent is the open source WinDirStat.

(I am inclined to try Daisy Disk next time as well, as it looks to be faster and with an interesting UI).
posted by Gomez_in_the_South at 10:10 PM on February 12 [1 favorite]

You can try this new app called hyperspace, that will clean up duplicate files. It could free up a substantial amount of space.
posted by rambling wanderlust at 3:49 AM on February 27