How to clear 173GB of System Data on MacBook Air?

If you have Time Machine enabled but haven't connected your external backup drive in a while, your Mac creates local "snapshots" on your SSD. These are categorized under System Data.

Open Terminal (search for it using Spotlight by pressing Cmd + Space). Paste the following command and press Enter:

tmutil listlocalsnapshots /

If you see a list of dates, it means local snapshots are present. To clear them, either connect your usual backup drive and let it complete a backup, or temporarily turn Time Machine off and back on in System Settings to force-delete them.

You have a Mac that started life with only 256 GB of storage, already behind the 8-ball in today's digital world. This will be an ongoing problem for you.

Here are some things that you can do everyday to manage your free space:

• Reboot your Mac at least weekly. Let the OS do housekeeping and clear caches.

• Empty the Trash in the Dock. 

• Empty the trash in the Photos app.

• Delete unused and unneeded application installers from your downloads folder and desktop. No need to store on your Mac what you can freely download again any time.

• Transfer files that you don’t use daily to an external drive and then delete them from the startup drive and empty the trash. Files that typically take up the most room are movies, images and music.

This from Apple on the subject of freeing up space:

Free up storage space on Mac - Apple Support

Find and delete files on your Mac - Apple Support

And this user tip: How to Use Finder to Clear “System Data" on a Mac (Thank you, @TheLittles!)

If you have enabled Time Machine to back up your Mac automatically but do not keep your backup drive connected all the time, then MacOS keeps a number of Time Machine snapshots on the drive as part of the backup process.  These TM snapshots can occupy a significant amount of drive space. You can disable the creation of these many TM snapshots by setting TM to backup manually rather than automatically at intervals.

You can view and manage these Time Machine snapshots in Disk Utility or in the Terminal app. View APFS Snapshots in Disk Utility on Mac - Apple Support 

You can also use apps such as Storeograph from Etresoft, Inc  or OmniDiskSweeper from Omni Labs  to find the large files on your drive.  Once you've located these larger user files, you can relocate them to another drive and/or delete them if they aren't needed.

Reducing System/Volume/Data is a very common question. 

Part 1 of 2

Detailed methods that may or may not work 

A -  System data taking too much in MacOS Sono… - Apple Community

B - Time Machine Local Snapshot won't delete - Apple Community

C - Over 60% storage blocked by System Data - Apple Community

D - Running out of storage - system data is huge after upgrade to macOS Tahoe 26.2

E - System Data consuming storage on Mac and how to clear it

F - System Data at 114 GB AFTER deleting other files....

G - How to free up System Data space on Mac

How to free up ‘System Data’ and other storage on your Mac from a fellow colleague  @ neuroanatomist

Use another application to see where space is being used  Storeograph  Directly from the Developer 

View APFS snapshots in Disk Utility on Mac

Stop Chrome Browser From Downloading a Hidden 4GB AI File

Suggest getting an External SSD Drive and start moving your Pictures, Videos, Music and any other large files you have control over, OFF the Internal drive and Onto the External

Part 2 of 2

Quick Fix ?

For Apple Silicon computers, use Disk Utility to erase a Mac. 

Use the Erase All Content and Settings feature to quickly and securely erase all settings, data, and apps, while maintaining the operating system currently installed

Always make a Time Machine backup before proceeding.

Migrate only the user account, not the entire system.

Reinstall only the necessary applications from the Apple App Store or directly from the developers.

SpiderMac wrote:

If you have Time Machine enabled but haven't connected your external backup drive in a while, your Mac creates local "snapshots" on your SSD. These are categorized under System Data.

Open Terminal (search for it using Spotlight by pressing Cmd + Space). Paste the following command and press Enter:

tmutil listlocalsnapshots /

If you see a list of dates, it means local snapshots are present. To clear them, either connect your usual backup drive and let it complete a backup, or temporarily turn Time Machine off and back on in System Settings to force-delete them.

FYI, it is possible to view APFS backup snapshots using the Disk Utility GUI interface at least with macOS 13.x Ventura & later (not sure which version of macOS added this ability to Disk Utility). No need to for the Terminal.

View APFS snapshots in Disk Utility on Mac - Apple Support