"System data" is taking up nearly 1TB of hard drive space

It's tough to tell since Apple now hides so many files, logs & caches are two things that can grow beyond belief, and the Storage Report is of no help usually.

Some things to look at, let usc know one way or the other please.

You may find neuroanatomist's User Tip helpful: What is "Other" storage on a Mac, and how can I clean it out? - Apple Community. 

Terminal code to clean DocumentRevisionsfolder…

https://apple.stackexchange.com/questions/313102/what-will-occur-if-the-documentrevisions-v100-folder-is-deleted

macos - What will occur if the .DocumentRevisions-V100 folder is deleted? - Ask Different (stackexchange.com)

Look for iOS backups…

/Users/YourUserName/Library/Application Support/MobileSync/Backup

OmniDiskSweeper shows you the files on your drive, largest to smallest, and lets you quickly Trash or open them.

https://www.omnigroup.com/more/

Purging local backups

Please note that although this doesn't affect your remote backup from Time Machine, this will get rid of the redundancy (at least until the next Time Machine backup) that a local backup disk will provide. If you need such redundancy or are worried about the recovery of your data then you would be best served to let macOS determine when to purge these files.

Start Terminal from spotlight.

At the terminal type tmutil listlocalsnapshotdates. 

Hit enter.

Here, you'll now see a list of all of the locally stored Time Machine backup snapshots stored on your disk.

Next you can remove the snapshots based on their date. I prefer to delete them one at at time. Once my "System" disk usage is at an acceptable level, I stop deleting but you can delete all of them if you want to reclaim all of the disk space.

Back at the terminal, type tmutil deletelocalsnapshots YYYY-MM-DD-HHMMSS , where will be one of the dates from your backup. This will be in the form of xxx-yy-zz-abcdef. Try to start with the oldest snapshot.

Hit enter.

Repeat for as many snapshot dates as required

http://www.thagomizer.com/blog/2018/03/27/cleaning-up-time-machine-local-snapshots.html

tmutil deletelocalsnapshots / # deletes all the snapshots

Thanks to BobHarris file sizes, Applications -> Utilities -> Terminal:...

sudo du -hx | sort -h 

sudo du -hx ~/| sort -h 

System Data used to be call the Other category in earlier systems. It can contain files that are not necessarily i the system folder but read out over the drive. The Other category 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

• Local Snapshot files from Time Machine

• 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 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 can 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 are no longer needed. 

Three things that can grow to use a lot of space:

Time Machine snapshots

Caches

Logs

You should be able to see if there are any snapshots by opening Disk Utility and setting View->All Devices

By starting in Safe Mode, you may get some space back from the clearing up of caches.

Logs are probably somewhere under /Library or ~/Library

I'd search for "big" files using the Finder, eg.

In Finder, press Command-Shift-G and paste ~/Library,

then do a search for big files (you may start with "greater than 1GB" for example, to see what appears);

also do a similar search under /Library or over all the mac.

Jeremy Bell2 wrote:

I deleted half of those TimeMachine snapshots, and I didn't notice any change in available space.

The data you deleted may still reside in every single other snapshot made prior to deleting the data. You will need to delete every snapshot up to the day you deleted that data before you will will see a difference.

Also, if any of the data you deleted was actually copied to another location within the same APFS volume, then you would need to delete both copies of that data before you would see any difference in the amount of Free storage space since the APFS file system does not make two separate physical copies of the data. Storage with APFS volumes is complicated.

Jeremy Bell2 wrote:

how can I fix this??

Just wait a couple of days. The files that you requested to be deleted will eventually be deleted by the system and the space they used will be recovered.

But I don't know how much data you deleted. You should delete at least 250 GB. Usually when this happens, people will obsess over a few kilobytes of data, searching for those few bytes that are most likely to corrupt some critical file system operation. Don't do that. Delete only files that you created. Don't touch anything in a "Library" folder.

Yes it has stumped many of us! :(

Apparently Apple has a new way of hiding files & more than a few find out the only way is to Backup, then Erase the Drive, or clone then clone back which seems to leave some huge temporary files behind!?

Carbon Copy Cloner seems to accomplish it...

http://www.bombich.com/software/ccc.html

The Grand Perspective comment is for those needing to free up space for one reason or another. The rest of the reply is describing what all that "junk" is. Some files may be listed as part of application and also system data. It really doesn't make a lot of sense but there it is.

I am having the same issue, but instead of 1TB, is taking all my 2TB of disk space, this is after I upgraded to Sonoma on my M1 Mac Studio.

On my other computer a MacBook Pro with Intel, also with 2TB of internal space, this is not a problem.

Super frustrating, this makes my M1 Studio unusable.

The System Data option is grayed out and you don't know what happened to it. From my own experience, it seems system data varies for different devices. My Mac only has 78 GB taken by system data.

👍