System Data and Free Space Changes in Golden Gate

TL;DR:

Rest assured that upgrading to Golden Gate did not result in the loss of 50-100 GB of your Mac’s precious storage space. 

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 those data are no longer counted as available space. They are also now included in System Data, accounting for the apparent increase many users have noticed. 

The full version:

Many users have noticed that upgrading to macOS 27 Golden Gate increased what macOS reports as ‘System Data’, and some users have also suggested that the upgrade resulted in significantly less free space on their internal storage. Note that the improved, locally-stored models for Apple Intelligence on Golden Gate do take up about 20 GB more space than those on Tahoe.

Many users report the ‘loss’ of substantially more than that. Rest assured that upgrading to Golden Gate did not result in the loss of 50-100 GB of your Mac’s storage.

There are several ways to check how much of your internal storage is available. Doing so periodically is a good idea, because 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). You can:

• Select your internal drive then click File menu > Get Info, check Available space
• Go to System Settings > General > Storage, check the graphical display at the top of the settings pane
• In Disk Utility (in Applications > Utilities), by selecting the main container disk below the drive itself (you may need to select View menu > Show all devices to see it)
• In the System Report – hold the Option key and click the Apple menu > System Information (the top menu item), look for the name of your internal drive (Macintosh HD, unless you have renamed it as I did)

On macOS 27 Golden Gate, all those methods report consistent values for available or free space.

That was not the case in versions prior to macOS 27. With Golden Gate, Apple finally addressed the somewhat confusing way space was reported on prior versions of macOS. Terminology is important here – free space was not the same thing as available space. On macOS Tahoe and before, what macOS showed in most places was available space. Available space included both free space and ‘purgeable’ space, the latter comprising system caches, snapshots and other data that macOS could delete if it decided more free space was needed. However, there was no way the user could force those data to be purged.

On pre-27 versions of macOS, Get Info on the internal drive and System Settings > General Storage showed available space, Disk Utility and the System Report showed free space, which was lower because it included ‘purgeable’ but was the correct value for how much space was really available on the Mac. For example, at a given point in time on my M4 MacBook Pro, the Storage settings pane and Get Info on the internal drive showed 1.24 TB of Available space, whereas Disk Utility shows there was 1.15 TB of actual free space, 90 GB less than ‘available’. Although 90 GB is a small fraction of my 2 TB internal storage, that would not be the case with 256 GB or 512 GB of internal storage.

Using Get Info on the internal drive clearly shows the difference – on Golden Gate, there is no reference to purgeable space that was found on Tahoe and before. 

This change makes sense, if anything it’s surprising that it took Apple so long to address this issue. Before Golden Gate, the maths didn’t math. If you add up the values reported above for Available and Used, the total is 2.07 TB – more than the capacity of the drive, because ‘purgeable’ was being counted in both used and available (the latter assuming it was actually purged, but it wasn't). Golden Gate reconciles that problem, and now free and available space mean the same thing. The sum of those two values for my Mac on Golden Gate is 1.985 TB (the remaining ~15 GB of space on the 2 TB drive is used by the preboot and recovery volumes).

As mentioned above, those ‘purgeable’ data are still being tracked by macOS, and starting with Golden Gate they are included in System Data. That change is what accounts for the reports of sometimes dramatic increases in System Data. On Tahoe, System Data on my personal Mac ranged from 9 to 40 GB. On macOS Golden Gate, it ranges from 120 to 160 GB. 

Keep in mind that ‘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.

Under the hood, macOS is still keeping track of those ‘purgeable’ data. I see evidence of this when I first open System Settings > General > Storage. As the categories are being calculated based on Spotlight, the ‘free’ space in the graphic at the top of the settings pane shows 1.24 TB, but a few seconds later once those calculations are complete, that value drops to 1.14 TB. That 100 GB wasn’t lost – it was never available to begin with, macOS just added what used to be called purgeable data to the total for System Data. 

Hope that helps clarify what’s going on with System Data and free storage space in macOS 27 Golden Gate. 

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