System Data Taking Over Half of My Mac’s Storage

Part 1 of 2

From your description, it appears this computer has the tiny 256 GB SSD drive which can not be replaced as it is probably Soldered onto the Logicboard

Be best you can do in Manage the available space

Remove the Disk Cleaner  as per the Developers Specific Instruction

CleanMyMac , aka “ BrickMyMac “

Part 2 of 2

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. 

System Data is typically between 50GB - 120GB and it fluctuates up and down. Here is what I see right now. What you are seeing is normal behavior with macOS Sequoia.

I know you don't want to hear this, but next time you buy a Mac, consider your internal storage needs. Apple isn't the only company selling small soldered internal storage on their base configurations to keep costs down for entry level light users. More and more laptops are doing it to save space and keep them thinner.

With the advent of cloud, it is now easy to sync to cloud storage and free space on the local disk. Cloud eliminates data migration from old to new. Users can also right-click files and choose to Free Space to remove the local copy and replace it with a pointer to the cloud file(s). Most all Cloud solutions have this functionality including iCloud Drive. If you use Apple's Pages, Numbers, Keynote then use iCloud. If you use 365 use OneDrive. If you are in Google's ecosystem use Google Drive.

Or for the ultimate in privacy you can use a NAS device, install NextCloud, Plex or Jellyfin for media and put Tailscale on it to have your own private cloud in your home/office and access it from anywhere in the world over the Internet. That way you own the storage and your data is private. Tailscale is a modern VPN mesh network layer that is always encrypted. You and only you hold the encryption keys, not even Tailscale can see your data. They just route the traffic. It can get around firewalls and NAT. It's free for 3 users and 300 devices. You can define any of your tailnet devices, such as the NAS to be an exit node. An AppleTV or RaspberryPi is ideal as they are always-on and draw very little power. Connecting to the exit node remotely gives you an Internet address that makes you look like you are at home/office and not traveling overseas in south east Asia for example. Using an exit node is like a traditional VPN solution. But it's not required to reach your Tailscale devices on the tailnet.

In favor of cloud storage, realize how often are any of us truly OFFLINE with no Internet? Even in a crisis, you can go to a retail shop and walk out with a SpaceX Starlink mobile dish and get online with decent speeds from most anywhere on the entire planet.

While shuffling external drives around and cloning them for backups is an option. It is tedious and relies upon you being extra diligent. Which is why I recommend cloud storage and/or private cloud storage.

I'm running into a similar issue and have pinpointed the issue to OneDrive. If you use OneDrive, that's likely the culprit.

From my understanding, what it boils down to is OneDrive is basically returning used space in two different places on your hard drive, at these locations:

~Library/CloudStorage

~Library/Group Containers/UBF8T346G9.OneDriveStandaloneSuite

One of these appears to be phantom used space, but as far as I can tell, there isn't really a known resolution. This thread has some suggestions, but that seems to be as good as it gets.

https://answers.microsoft.com/en-us/msoffice/forum/all/onedrive-takes-massive-storage-in-system-data-on/6dc11cab-3fe9-401a-8bbd-7e015f601c2e

This thread seems to be the one that announced the changes that essentially caused this issue. Feel free to doomscroll the comments.

https://techcommunity.microsoft.com/blog/OneDriveBlog/inside-the-new-files-on-demand-experience-on-macos/3058922?after=MjQuMTF8Mi4xfGl8MTB8MTMyOjB8aW50LDQwNTI5MDYsMzY4MzgwMA

There is the Operating System denoted by macOS = 28.33 GB

This is the user account denoted by System Data = 106.72 GB

Total of about 130 GB

The other alternative

Explore the Apple Trade-In  Process where the Value of the exiting device could be used against the cost of a new Apple Computer, iPhone or iPad 

Notation - Some devices and depending on the computers age may have little to no value at Trade In time.

But at least the device will not arrive to the Land Fill Site and be recycled in a responsible way by Apple

Or Shop Refurbished Apple computers at an Apple Reduced Cost

Have used both previously and have been satisfied each time.

System Data used to be called "Other" category in previous systems and is a potpourri of files which can include:

• System temporary files

• macOS system folders

• Archives and disk images (.zip, .iso, etc. - often found in the Downloads folder)

• Personal user data

• Files from the user’s library (Application Support, iCloud files, screensavers, etc.)

• Cache files: browser, Mail

• Mail messages & attachments

• Fonts, plugins, extensions

• Safari reading list

• iTunes backups

• Crud resulting from jailbreaking your iDevice

• Game data

• Saved data files

• Call history

• Notes

• Media

• Voice memos

• Other files that are not recognized by a Spotlight search

• Media files that cannot be classified by Spotlight as a media file because they are located inside of a package

• Files created and modified by other user accounts on your Mac.

They can be located anywhere on your hard drive.

The files that you have control over are located in the Documents, Downloads, Pictures, Music and Movies folders.  You can use either of these two free apps, GrandPerspective  or OmniDiscSweeper, to find the largest files on your drive so you can determine if they can be deleted or moved to an external HD for storage.  

Note: you can empty the Downloads folder after the apps and/or updates that were downloaded have been installed or applied.  Many users have found a couple of Gigabytes of files in their Downloads folder which are no longer needed. 

Another source of potential free space is removing the local Time Machine snapshots from your boot drive. That can be accomplished using Disk Utility. This screenshot tells the tale that I experienced:

I always leave the latest snapshot for safety's sake.

For some reason system data continues to grow over time even if nothing has been added by the user. Recently my system data doubled over time. I went into recovery, erased my drive, reinstalled the OS and then migrated data back. That cut my system data by 50%. But as always it starts to grow once again.

StaticRevo wrote:

I see, so the only real option is to erase everything again in reality. If it keeps on increasing at this pace it will take over my entire disk in no time.

The solution is to identify what is causing the problem and correct it. Years ago, the only thing that ever caused this was Time Machine snapshots. But these days, that's actually pretty rare. It seems that every 3rd party app, and many Apple AI tasks, just eat storage like it's going out of style.

Unfortunately, with 100 GB in System Data, you're not even close to "outrageous" territory. That's relatively good.

StaticRevo wrote:

That would have been okay if I had a larger storage capacity, but from my 245GB of storage 130 of them are taken up by seemingly nothing.

Sadly, a limitation on the amount of available physical storage will not limit the amount of System Storage. You could get more than 245 GB. 😄

With a 250 GB, you have to watch your storage like a hawk. Be brutal. You'll need a 3rd party storage management tool. You'll have to become intimately familiar with all of the apps on your computer that are likely to create files in various hidden system directories.

Those "clean up" and "optimize" tools are NOT going to help. This problem is NOT caused by cache files or "junk" files.

Just as a data point, I have a Mac mini 2024 with a 512GB drive and my System Data is currently sitting at 34.86GB. I've no idea why mine should be so much lower than the original poster's, or vice versa, why his should be so much higher than mine, so some more clarity from Apple would be helpful.

You probably already know this 👍

Perhaps this maybe helpful to OP

Apple Intelligence in Sequoia 15.2 does take up about 4.85 GB of space in addition to the Operating System