User profile for user: Colin Foster
Colin Foster Author
User level: Level 1
80 points

Why does my MacBook Air keep losing disk space?

I usually have about 60GB free on a 500GB drive (on a MacBook Air M2/16GB) but since upgrading to Sequoia (15.4.1) I keep getting "your almost out of disk space" warnings(< 5GB space remaining), and all my iCloud based files unload to make room for whatever is chewing up the disk.


Without making any changes, all the space suddenly frees up after 20 minutes or so, and I'm back to 40GB (then some time later it might revert to 60GB when I'm not looking). Each time I have to re-download all my iCloud-based files to make sure they are available when I need them. This seems to happen about once per day.


I can see through Little Snitch that the network is very busy chatting with Apple / iCloud with Apple and AmazonAWS through "NetworkServiceProxy". (I think that was the name -- it's no longer visible.)


Anyone have any idea what's happening?



[Re-Titled by Moderator]

MacBook Air, macOS 15.4

Posted on Apr 20, 2025 5:56 AM

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User profile for user: etresoft
etresoft
User level: Level 9
56,326 points

Posted on Apr 20, 2025 8:19 AM

Colin Foster wrote:

I'm not sure I understand why "too little disk space" (60GB of 500 is 12%) would cause the disk to fill up *more* (to only 1% free)? Historically I might start thinking about freeing up disk space if it went under 40GB but otherwise not worry about it and there's never been an issue.

Some clarification is necessary. You said you had "60GB free" and then referenced "1% free". Where are you getting these values from? Most people see various places in the operating system where it displays storage values and identifies a certain amount as "available". A normal person's brain automatically translates that "available" to "free".


But Apple developers think that you'll worried if you saw your free disk space go below 100 MB. They don't want you to be worried. They want you to be happy. So instead of displaying "100 MB free", it simply displays "60 GB available".


And clearly, you were very happy with that value. Technically, it's true. You do have that much space available if the system really needed it. Of course, the system does need it, so every day, it deletes those iCloud files. And every day, you click the little cloud button and download them again. Then you run out of free space and all those files go away. Lather, rinse, repeat.


Is there any way to get insight into what's hiding in the 70GB of "System Data" listed on the storage graph?

It's called "data".


What we have here is a failure to communicate. The system is trying to tell you that you should have purchased a bigger hard drive. Forget about the 70 GB. That's not important. The operating system needs at least 100 GB of truly "free" store to be happy. You can check your free storage in Disk Utility - and pretty much only Disk Utility. Ignore anything that says "available".


If you had 100 GB free, then that would be adequate for normal usage. The 70 GB of "system data" fits with a little room to spare. So the question is, what are you using that other 400 GB of storage for? That where you need to trim the fat. Find the files that you don't need every day and either move them to iCloud or an external archive drive. Make sure you enable "optimize" in iCloud Drive. Next time, get a 1 TB drive.

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User profile for user: etresoft
etresoft
User level: Level 9
56,326 points

Apr 20, 2025 8:19 AM in response to Colin Foster

Colin Foster wrote:

I'm not sure I understand why "too little disk space" (60GB of 500 is 12%) would cause the disk to fill up *more* (to only 1% free)? Historically I might start thinking about freeing up disk space if it went under 40GB but otherwise not worry about it and there's never been an issue.

Some clarification is necessary. You said you had "60GB free" and then referenced "1% free". Where are you getting these values from? Most people see various places in the operating system where it displays storage values and identifies a certain amount as "available". A normal person's brain automatically translates that "available" to "free".


But Apple developers think that you'll worried if you saw your free disk space go below 100 MB. They don't want you to be worried. They want you to be happy. So instead of displaying "100 MB free", it simply displays "60 GB available".


And clearly, you were very happy with that value. Technically, it's true. You do have that much space available if the system really needed it. Of course, the system does need it, so every day, it deletes those iCloud files. And every day, you click the little cloud button and download them again. Then you run out of free space and all those files go away. Lather, rinse, repeat.


Is there any way to get insight into what's hiding in the 70GB of "System Data" listed on the storage graph?

It's called "data".


What we have here is a failure to communicate. The system is trying to tell you that you should have purchased a bigger hard drive. Forget about the 70 GB. That's not important. The operating system needs at least 100 GB of truly "free" store to be happy. You can check your free storage in Disk Utility - and pretty much only Disk Utility. Ignore anything that says "available".


If you had 100 GB free, then that would be adequate for normal usage. The 70 GB of "system data" fits with a little room to spare. So the question is, what are you using that other 400 GB of storage for? That where you need to trim the fat. Find the files that you don't need every day and either move them to iCloud or an external archive drive. Make sure you enable "optimize" in iCloud Drive. Next time, get a 1 TB drive.

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User profile for user: leroydouglas
leroydouglas
Community+ 2025
User level: Level 10
198,972 points

Apr 20, 2025 6:58 AM in response to Colin Foster

Colin Foster wrote:

I usually have about 60GB free on a 500GB drive (on a MacBook Air M2/16GB) but since upgrading to Sequoia (15.4.1) I keep getting "your almost out of disk space" warnings(< 5GB space remaining), and all my iCloud based files unload to make room for whatever is chewing up the disk.

Without making any changes, all the space suddenly frees up after 20 minutes or so, and I'm back to 40GB (then some time later it might revert to 60GB when I'm not looking). Each time I have to re-download all my iCloud-based files to make sure they are available when I need them. This seems to happen about once per day.



Your drive is essentially choked full.

SSD need to have 15-20% free storage if not 25% at all times to work efficiently. I'll let you do the math.



“free” space is the "available" minus the "purgeable"

macOS does not readily release that "purgeable" space, but on its own schedule...



Data deleted on an SSD will not be available immediately until the SSD resets storage and makes it writeable. If you do not shut down you may see it as free space as soon as 12-24 hrs.



How to free up storage space on your Mac - Apple Support

Free up storage space on Mac - Apple Support



etresoft maybe said it best summed up here—


“The "available" storage is the amount of used storage that the operating system could automatically delete if it felt that it was really necessary. The "free" storage is the amount that you can actually use for something.

There are system processes that run in the background and automatically delete some of the "available" storage and convert it to "free". If you completely run out of storage, then those system processes will try a little harder. When you "delete" files you are just hinting to the operating system that you don't need those files anymore. The operating system will eventually remove them, but on its own schedule."


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User profile for user: Colin Foster
Colin Foster Author
User level: Level 1
80 points

May 6, 2025 2:25 PM in response to Colin Foster

UPDATE: When this starts, I can watch my disk gradually fill up (about 5 GB/minute).


BUT, as soon as I launch the "Storage" panel in System Preferences, the system immediately stops filling up my disk and frees up whatever it had used (restoring it to 50-60GB free in less than a minute).


Scanning with Omni Disksweeper before and after launching the Storage System Preferences shows no difference between the two. ¯\_(°-o)_/¯

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User profile for user: Colin Foster
Colin Foster Author
User level: Level 1
80 points

May 12, 2025 7:49 AM in response to Colin Foster

I have tried Find Any File (when the disk space was depleted), looking for anything that was modified in the last 5 minutes that's greater than 20MB and it found nothing interesting (a handful of files).


If curious, here's a video of the disk space gradually being released when the "Storage" option in System Preferences starts trying to figure out where the disk space is being used:

https://ext.runcode.run/disk-fill-and-release.mp4

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User profile for user: Colin Foster
Colin Foster Author
User level: Level 1
80 points

Apr 20, 2025 7:11 AM in response to leroydouglas

Thanks for the thoughts.


I'm not sure I understand why "too little disk space" (60GB of 500 is 12%) would cause the disk to fill up *more* (to only 1% free)? Historically I might start thinking about freeing up disk space if it went under 40GB but otherwise not worry about it and there's never been an issue.


Is there any way to get insight into what's hiding in the 70GB of "System Data" listed on the storage graph?

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User profile for user: Colin Foster
Colin Foster Author
User level: Level 1
80 points

Apr 20, 2025 1:34 PM in response to etresoft

If the "free" stat from the System Information app is the kind of free you're talking about, free and available are pretty much in sync with each other. Most of the time I have 60GB (12%) free. The system now seems to randomly start using up that space until there's less than 5GB (1% of 500GB) available/free.


So what I'm not clear on is why (when it's never been an issue before with even less disk space free than now) the system thinks "oh no! There's so little space left! I had better start using it up!" until there's so little it has to dump iCloud files off the system. I'm not in the middle of compiling software, rendering in Blender or anything like that. The "available" number just drops minute-by-minute, dumps icloud files, and then it gradually recovers.


Also, I get that systems need some swap space but it makes no sense that an operating system installed on a 250GB drive can get by 100% happy with 50GB free (20%) but when on a 1TB drive now needs 200GB free or it's going to be "choked".


(FWIW, I booted into safe boot mode and back to regular boot, and that has freed up 10GB of something from System Data.)

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Why does my MacBook Air keep losing disk space?

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