How do I identify the 100GB of System Data on my MacBook Pro?

My 2¢ on the subject:

The System Data used to be called the Other category which 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.

Just what you've already been made aware of. 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 this free app, GrandPerspective, 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 should empty the Downloads folder after the apps and/or updates that were downloaded have been installed or applied.  Some users have found a couple of Gigabytes of files in their Downloads folder which were no longer needed. 

kp229qw wrote:

It's a well documented problem that system data balloons to over a 100GB. Im curious as to why?

It's not system data. It's just other random data that the system can't categorize.

I have deleted all local Time Machine backups, old install files, developer cache, data from deleted programs etc and it's still over 100GB (overall it made little effect).

It wouldn't be any of that.

Im wanting to set up a Multipass VM

You have a 250 GB hard drive. That's way too small for any VM.

Is the best solution to just wipe the Mac?

That will work, but only if you don't put back all the data.

surely fresh installs of MacOS don't come with 100GB of unexplained and seemingly unfindable files?

No and yes. Fresh installs do not come with 100 GB of data. However, when various apps create this kind of data, they always store it in places where the standard system file searches don't cover, or the files themselves aren't recognized by the system, hence their being treated as "system data" in the first place.

I don't understand why these files may be "needed" for the OS.

They aren't needed by the operating system.

I'm really not very clued up on this sort of thing so I would just like to learn. Any help or insight would be greatly appreciated. (I know that a quarter of terabyte was a silly under-spec in hindsight, at the time I was unaware of the sort of space system data takes up)

Remember, it has absolutely nothing to do with the "system". What you need is some 3rd party disk storage analysis tool. There are several available. I can't recommend one because I develop one myself and I'm not going to recommend competing products that are more dangerous than my own.

The trick is that you have to locate these files. More importantly, you have to identify the source of the files. If you don't find the source, this problem will just repeat itself forever. There are many possible sources. Years ago, it was always Time Machine local disk snapshots. But recently, it is more likely to be 3rd party apps running amuck.

kp229qw wrote:

It's a well documented problem that system data balloons to over a 100GB. Im curious as to why? I have deleted all local Time Machine backups, old install files, developer cache, data from deleted programs etc and it's still over 100GB (overall it made little effect).

Im wanting to set up a Multipass VM but I'm going to struggle to allocate sufficient space if I can't find out what this 100GB actually consists of. Is the best solution to just wipe the Mac? surely fresh installs of MacOS don't come with 100GB of unexplained and seemingly unfindable files? they didn't last time I wiped with Monterey. I don't understand why these files may be "needed" for the OS. I'm really not very clued up on this sort of thing so I would just like to learn. Any help or insight would be greatly appreciated. (I know that a quarter of terabyte was a silly under-spec in hindsight, at the time I was unaware of the sort of space system data takes up)

https://discussions.apple.com/content/attachment/538f17e7-7ed4-4645-b311-e654fd3102ae

To get a better overview of Space Used versus Empty Space

Use Disk Utilities

System Data: Contains files that don’t fall into the categories listed here. This category primarily includes files and data used by the system, such as log files, caches, VM files, and other runtime system resources. Also included are temporary files, fonts, app support files, and plug-ins. 

You can't manage the contents of this category. The contents are managed by macOS, and the category varies in size depending on the current state of your Mac.

There is Purgeable Space and there is Empty Space.

They are not one and the same.

Purgeable Space which is Controlled by the Operating System. When the Operating Systems decides the computer needs additional Empty Space, it will move a portion of the Purgeable to Empty space

AFAIK - there is no User Actions to hasten this transition from Purgeable to Empty Space

It can day or longer before this will occur.

The links below will help in identifying what is taking up space on the Internal Drive.

It will also provide possible ways to remove data that is under the direct control of the User ( Home Folder ) . 

Rebuild the Spotlight index on your Mac

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

Free up storage space on your Mac

GrandPerspective 

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 there a Suite of Adobe Applications  used on this computer ?

They may create some very large cache files that can be removed. Though, the Adobe cache files will be recreated as the Applications needs 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 

kp229qw wrote:

I see I think I have some pretty good guesses to be fair. Am I allowed to ask which one you develop? You clearly know your stuff.

I'll give you three guesses and the first two don't count.

****, that is a surprise to me. Im just launching an ubuntu instance to use some open source CFD software (openFOAM), on their website they use a 100GB VM saying its plenty, I may have been misled.

But you only have 250 GB to start with. Plus, it's likely that your 100 GB of "system data" is your 100 GB VM.

Would adding an external drive work?

Sure. Just remember that external hard drives are often going to be much slower than the internal drive. But a high quality external SSD is still going to be plenty fast. I recommend using APFS for the format. Don't try anything fancy like changing your boot drive or your home directory. That won't end well.

Realistically I don't think the laptop is the choice for this XD I was just excited by the arm optimisation of the software.

I remember when Apple first introduced the Apple Silicon chip. People seemed super-excited to run VMs on it. I couldn't understand why. Apple isn't in the business of supporting other people's operating systems. If you want to run something on an Ubuntu VM, Apple hardware is not the right choice.

Not being a Developer like the previous contributor

Is do see listed Developer listed using 329.45 MB

Not really a lot of used space but what the Developer Software does, that I can not help with

Perhaps the other contributor maybe able to shed some light and how that may apply to the computer issue ?