MacOS 27 System data using 50% of disk space.

Hello,

This is normal for users who have updated to MacOS Golden Gate 27. Spotlight is rebuilding itself and it's Spotlight Index. Just leave it as it will soon complete and the 'System Data' will go down again.

The reason your System Data increased when you upgraded to Golden Gate is that Apple changed how space usage is calculated by macOS. Spotlight indexing will not change System Data. With macOS 27 Golden Gate, Apple reconciled the apparent discrepancy of available space vs. free space. Prior versions of macOS reported system caches, snapshots and some other data as ‘purgeable’, though the user had no control over the purging. Those data were not included in System Data in versions of macOS prior to Golden Gate.  

On macOS 27, separate ‘purgeable’ space is no longer reported, and instead those data are now considered as used space. They are also now included in System Data, accounting for the apparent increase you (and others) have noticed. You didn't lose space, macOS just categorizes differently now than on Tahoe.

Lots more detail on this change shown in this User Tip:

System Data and Free Space Changes in Gol… - Apple Community

The best advice is to just ignore the System Data category. ‘System Data’ is merely a catch-all category for files that Spotlight cannot assign to specific categories like Applications, Documents, Photos, etc. In fact, what is now shown as System Data used to be reported as ‘Other’, Apple changed the label in macOS 12 Monterey. System Data probably sounds better, but Other was closer to reality.

As a rule of thumb you should aim to have 15-20% of your total internal storage as free space (~20-25 GB as an absolute minimum). If you do not have enough free space on your Mac’s internal storage, then 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

I reduced my "system data" by simply restarting my computer. However I would first let Golden Gate go at least another day to do post-install housekeeping.

However, yours suggests something else is going on. My Macbook Pro 2024:

My Mac has no useless utilities installed like anti-virus, so-called "cleaning" apps, or "retail" VPNs. All those can demand overhead and increase workload.

Also use Disk Utility to check for a build-up of APFS snapshots, cause whe a Time MAchine drive is left disconnected:

View APFS snapshots in Disk Utility on Mac - Apple Support

Two snapshots are normal. If more are shown, delete all except the last two.

In the face of newer, larger OS versions, 256GB drives are approaching obsolescence. We up-order our Macs with more storage to help with "future-proofing."

tbirdvet wrote:

When I updated to OS27 my system data went from 45 to 121GB. I'm not worried as I have a large drive but found that an interesting jump.

That happened because what macOS formerly called ‘purgeable’ data was counted as both available space and used space, and now those data are classified as System Data (increasing that significantly) and counted only as used space (decreasing what is reported as available space, but leaving free space unaffected).

Lots more detail on this change shown in this User Tip:

System Data and Free Space Changes in Gol… - Apple Community

solafide wrote:

I assume 8 days should be enough for Spotlight to rebuild.

It is. However, Spotlight is only relevant because it powers that awful System Settings > Storage display. I recommend people avoid that misleading display altogether.

Spotlight was rewritten in macOS 27. Too early to say if it's any better. But any Spotlight problems are probably unrelated to storage problems.

Not only had the System Data increased substantially, but when I deleted a bunch of junk emails yesterday and today, the System data has jumped a lot and remains at that level.

Yes. That would be expected. Deleting files will always increase "System Data". That's because the files aren't deleted, they are just recategorized as "System Data". Later, within a day or two, the system will do some kind of regular purge of "System Data" and the space for those deleted files will be freed up.

Note that I hesitate a bit when describing that "purging" action. I just want to emphasis that it is much, much less thorough that the word "purge" might suggest.

Just today it jumped from 743 GB to 1.04 TB (right after I deleted the emails)

Did you delete 250 GB of e-mails?

I did download CleanMyMac to try but don't find it that helpful and will be deleting it. I do have third party VPN to use when on unsecured networks. I have had it for years and it has never caused System data bloat. I did delete old caches and logs and excess TimeMachine snapshots - this did not move that System data bloat at all - if anything, it may have grown a little.

I understand that CleanMyMac and VPNs are considered the devil's own software on this forum. I don't share that opinion. VPNs are definitely unrelated to this issue in any way. Generally speaking, any kind of 3rd party interference in system behaviour is going to cause problems. Manually performing any kind of system maintenance, or having some "clean up" app do it for you will only reduce performance, increase "System Data", and cause a wide array of bugs and reliability issues.

Caches are designed to improve performance and should not be deleted. These massive amounts of "System Data" are caused by some kind of low-level bug in macOS or some 3rd party system modification. Years ago, it was always Time Machine snapshots that caused it. That's still possible, but usually it's some other problem.

If you have a massive amount of "System Data", the only solution is a 3rd party storage management tool. The "Storage" tool in System Settings will not help. It will only confuse and enrage. Even with a 3rd party storage management tool, you may need help from people here in the forums regarding which files are safe to delete and which are not.

This is normal for users who have updated to MacOS Golden Gate 27. Spotlight is rebuilding itself and indexing. Just leave it for a few days as it will soon complete and the System Data will go down again.

I upgraded to macOS 27 on October 24th. I assume 8 days should be enough for Spotlight to rebuild. There are some strange things going on. Not only had the System Data increased substantially, but when I deleted a bunch of junk emails yesterday and today, the System data has jumped a lot and remains at that level. Just today it jumped from 743 GB to 1.04 TB (right after I deleted the emails) - over half my 2 TB drive. This is a 2020 13" M1 MacBook Pro. I have restarted. No difference. I did download CleanMyMac to try but don't find it that helpful and will be deleting it. I do have third party VPN to use when on unsecured networks. I have had it for years and it has never caused System data bloat. I did delete old caches and logs and excess TimeMachine snapshots - this did not move that System data bloat at all - if anything, it may have grown a little.

The_Council wrote:

This is normal for users who have updated to MacOS Golden Gate 27. Spotlight is rebuilding itself and indexing. Just leave it for a few days as it will soon complete and the System Data will go down again.

Sorry, but that is simply not true. macOS calculates System Data in a different way on Golden Gate than on prior versions of macOS. System Data is larger now, because it includes what used to be called 'purgeable' data.

Everyone is having this problem pretty much. My system data ballooned by 30GB in the last hour for no discernible reason. I'm sure it will be fixed with a software update somewhere down the line.

When I updated to OS27 my system data went from 45 to 121GB. I'm not worried as I have a large drive but found that an interesting jump.

Thanks. Makes sense now.