Available Disk Space on my MacBook Pro dropped

Manage Storage

Apple’s final word on managing the “System Data” category:

System Data: Contains files not listed here. It includes system files like log files, caches, VM files, and runtime resources. Temporary files, fonts, app support files, and plug-ins are also included.

You can’t manage this category’s contents. macOS manages them, and the size varies based on your Mac’s state.

Users have control over the User Account Folder (Home Folder). All other areas are inaccessible.

It’s good computer practice to keep at least 20% to 25% of the total drive capacity empty to avoid unintended consequences.

Purgeable Space is controlled by the operating system. When the system needs more empty space, it moves some purgeable space to empty space.

There’s no user action to hasten this transition. It can take days or longer.

The links below help identify what’s taking up space on the internal drive and provide ways to remove user-controlled data (Home Folder).

Rebuild the Spotlight index on your Mac.

What is “Other” storage on a Mac, and how can I clean it?

Free up storage space on your Mac.

GrandPerspective

How to delete Time Machine snapshots on your Mac.

This often occurs if the Time Machine Drive isn’t attached to the computer and TM Backup is set to run on a schedule.

TM Backup makes snapshots on the internal drive until the Time Machine Drive is attached. Then, the snapshots are transferred to the external drive.

View APFS snapshots in Disk Utility on Mac

See used and available storage space on your Mac.

Locate backups of your iPhone, iPad, and iPod touch.

If you use a suite of Adobe applications on this computer, they may create large cache files that can be removed. However, the Adobe cache files will be recreated as the applications need them.

https://helpx.adobe.com/ca/premiere-pro/kb/clear-cache.html

The same clearing of System Cache files can be achieved by booting into Safe Mode. They will be recreated as the system requires. 

Kimberly Beattie1 wrote:

I just realized that my available disk space just dropped from my usual 150GB (on the internal 500gb MB drive) to around 20GB.

Any other thoughts?

Yes. Two things:

#1 "System" is controlled by macOS. It will grow/shrink as required as necessary. One of the biggest contributors to (temporary) growth is Time Machine (TM.) Whether or not, you have a connected backup destination drive attached to your Mac, TM will create a local snapshot of your whole system's data folder when the backup is initiated. These, in theory, are trimmed over time, but they still take up a considerable amount of space. It is NOT recommended to manually delete them, even though you can.

You can verify that these snapshots exist by using the Disk Utility, as follows:

1. Run the Disk Utility, located in /Applications/Utilities.
2. From the Disk Utility menu bar, select: View > Show All Devices
3. From the same menu bar, select: View > Show APFS Snapshots
4. Select your data folder, listed under Internal. It could be named something, like Macintosh HD - Data, or simply, Data.
5. You should now see a new section at the bottom with a list of any current snapshots.

#2 macOS does not need any type of "cleaner" apps. Using them can and will cause more issues than resolve, especially when not carefully used. I encourage you to remove any from your Mac. We see many posts here with folks that use them and ask for help when they do.

Kimberly Beattie1 wrote:

So do I just wait it out to regain my storage?

Yes.

Also, the only useful storage indicator is the Free storage space value shown in Disk Utility. Ignore the "Available" storage value since it is very misleading....it is unfortunate Apple has put that misleading value everywhere in macOS and only shows the more important Free space value in Disk Utility or the Apple System Profiler.

Free space = Available space - Purgeable space

Available space = Purgeable space + Free space

Purgeable space is storage that macOS will at some unknown point in the future delete and is not controllable by the user other than deleting APFS snapshots although that will affect the backups. APFS snapshots will be automatically deleted at some point,.

Free space is storage that can be used immediately which is why this value is the most important one

It is so hard to talk about storage without using the word "available" since that has special meaning in macOS.

Any Third Party Applications that will interfere with the normal operation of the OS,  is an invitation for disaster. 

Certain Applications maybe available on the Apple Apps Store - this only means the Developer is prepared to pay Apple a percentage on each sale. 

What the Application may do to the computer is up to the User to check this out before purchase

Any of the below should be removed as per Developers Instructions 

Disk Cleaner 

CleanMyMac , aka “ BrickMyMac “

Looks like PRP_53 got back to you before I could and I concur those replies.

+1

Tesserax wrote:

+1

+2

Well there you go ... good find! I'm glad you got it worked out.