System data on MacBook Air increased to 96GB after Golden Gate update

"System Data" comprises your data, but they are files that Spotlight cannot assign to a specific category like Documents or Applications. Examples include Outlook attachments, Cloud storage caches, and Time Machine snapshots. 

Follow the steps in this User Tip:

How to free up ‘System Data’ and other st… - Apple Community

System Data can be kept to a reasonable amount, for example on my personal Mac it is around 21 GB right now (it's varied from 9 GB to 40 GB over the past weeks).

However, on my work Mac where I use MS Outlook heavily, it is well over 100 GB (in large part due to inline email attachments stored in the Library, as described in the above-linked User Tip).

Here are some steps to take to safely free up space:

Free up storage space on Mac - Apple Support

Optimize storage space on your Mac - Apple Support

How to free up ‘System Data’ and other st… - Apple Community

One important thing to know about "System Data" is that it is based on Spotlight indexing, and after a macOS update your Mac will rebuild the Spotlight index. That process can take some time.

About Spotlight indexing and search results on Apple devices - Apple Support

Let it complete, and if that doesn't help you can initially force a re-index manually:

Rebuild the Spotlight index on your Mac - Apple Support

From there, proceed to the steps here:

How to free up ‘System Data’ and other st… - Apple Community

A change in System Data from 25 GB to 96 GB after upgrading your MacBook Air to macOS 27.0 (Golden Gate) does not, by itself, indicate a problem.

Apple describes System Data as a general category containing files that do not fall into other storage categories, including system files, caches, log files, virtual-memory files, temporary files, and other system resources. 

Its size can vary depending on the current state of the Mac, and macOS manages its contents. (Apple Support)

The 96-GB figure therefore does not by itself establish whether the increase is temporary, permanent, or specifically caused by the macOS upgrade. 

I would not manually delete files from System Data.

After the upgrade has completed, restart the Mac and check System Settings >> General >> Storage again. 

Pay particular attention to Available storage. 

If you have plenty of available space, the System Data figure alone may not require any action. 

If available storage is significantly reduced or continues to decrease, the storage usage can then be investigated further.

Apple's guidance is available here: Free up storage space on your Mac and Change Storage settings on Mac.

Use another application to see where space is being used DaisyDisk 

View APFS snapshots in Disk Utility on Mac

Stop Chrome Browser From Downloading a Hidden 4GB AI File

From a fellow contributor How to Use Finder to Clear “System Data" … - Apple Community

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

lobsterghost1 wrote:

I don't spend much time in this MacOS forum, so if you see anyone else having an issue with System Data not returning to a normal level after updating, you might want to let them know reinstalling the OS helps.

Alternatively, just ignore it. Keep in mind that System Data is just the catch-all for items that Spotlight is not assigning to specific categories. Before the upgrade to Golden Gate, my Mac had about 850 GB used on the 2 TB internal storage, and System Data was around 25 GB. After the upgrade, my System Data is showing as ~165 GB. But the internal storage is still at ~850 GB. System Data went up by 140 GB, but that's just a category. It's not like there is an extra 140 GB of data on my drive because of the upgrade.

lkrupp wrote:

smartblondegirl wrote:

System data went from 25GB to 96GB after updating to Golden Gate on Macbook Air--is this normal?

After a major update the answer is yes, that’s normal. It should drop as time progresses.

In my case, after updating yesterday to MacOS 27, system data on my MacBook Pro jumped up significantly. I had hoped it would decline some at least by this morning, but it didn't. So I simply reinstalled MacOS 27 and that immediately returned my system data to a normal level. I don't spend much time in this MacOS forum, so if you see anyone else having an issue with System Data not returning to a normal level after updating, you might want to let them know reinstalling the OS helps.

I wound up calling Apple and had a great session with a MacOS advisor. He went through all the things which are in System Data and it turns on my iCloud Drive and One Drive are taking up most of the System Data and he said my Mac is indexing all of the data. Nothing seemed out of line and he theorized it will go down on it's own once everything finishes indexing, which could take days.

smartblondegirl wrote:

System data went from 25GB to 96GB after updating to Golden Gate on Macbook Air--is this normal?

After a major update the answer is yes, that’s normal. It should drop as time progresses.

neuroanatomist wrote:

lobsterghost1 wrote:

I don't spend much time in this MacOS forum, so if you see anyone else having an issue with System Data not returning to a normal level after updating, you might want to let them know reinstalling the OS helps.

Alternatively, just ignore it. Keep in mind that System Data is just the catch-all for items that Spotlight is not assigning to specific categories. Before the upgrade to Golden Gate, my Mac had about 850 GB used on the 2 TB internal storage, and System Data was around 25 GB. After the upgrade, my System Data is showing as ~165 GB. But the internal storage is still at ~850 GB. System Data went up by 140 GB, but that's just a category. It's not like there is an extra 140 GB of data on my drive because of the upgrade.

If my total storage was unchanged after the upgrade to 27, I wouldn't have been concerned. But my total storage on my MacBook Pro increased by about 100 GB with the increase in System Data. Reinstalling MacOS 27, brought my total and System Data back to the level it was before the update.

I did a simple reinstall of the OS, without affecting anything else on the MacBook Pro. If you power off your Mac, then hold the power button down until restore options appear, then choose you, you can simply reinstall the OS. Here's a link you can use to guide you --> How to reinstall macOS - Apple Support

It suggests it will take about 2+ hours, but is much faster.

EDIT: I just checked and again System Data and my overall Storage went right back up 100GB from before MacOS 27. My reinstall of MacOS 27 was not successful for more than a few minutes, so I'm just going to not pay attention to it and hope it adjusts on its own.

You're welcome. It turns out there are many things which are included System Data. iCloud Drive is a biggie. Services like Microsoft One Drive is another. Adobe Cloud if you have that is also included along with many other things.

lobsterghost1 wrote:

Reinstalling MacOS 27, brought my total and System Data back to the level it was before the update.

When you say "reinstalling MacOS 27," was that a simple reinstall via Recovery where you reinstall over the existing OS without charging anything else? Or did you do a complete wipe/erase clean install (e.g. what one does to "prepare a Mac for transfer or sale") and then migrate from a backup?

This whole "System Data" thing on Macs has been unhelpful for some years now. It didn't even finish calculating for some of the categories (including System Data) on my Mac until I upgraded to Tahoe and then it started working again, or at least showing numbers. Although I still can't figure out what is included in some of them -- I have multiple large Photos Libraries all in the Pictures folder and it seems like the "Photos" category in the Storage tool only includes the main System Photos Library and all the others get parceled out to the Documents or System Data categories.