System data suddenly fills up storage and empties after restart

I normally have 70 GB of free storage on my M1 Macbook Air 2020. Every week, the system data files inflate gradually filling up the 70 GB of free storage and blocking all functions. Once I restard the computer, the 70 GB are free again, and the same circle repeats. This has happened for the last 4 months. Please fix this Apple. Thank you.

MacBook Air 13″

Posted on Aug 18, 2025 04:43 AM

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3 replies

Aug 18, 2025 05:07 AM in response to Palamede

This is a peer to peer group. You are not addressing Apple here in the Community, only other users like yourself.


It sounds like you have a drive that has insufficient capacity for your needs. Apple could not fix this for you. It will be your task to copy enough of your data to an external drive that you can remove it and free up the space on your startup drive to avoid this issue.


What is the capacity of your startup drive?

Whatever it is, you’re stuck with it as the Apple Silicon Mac’s storage cannot be upgraded after purchase.


It is possible to use an external ssd as a startup drive, but of course that complicates using a laptop computer.



Aug 27, 2025 12:49 AM in response to D.I. Johnson

Thank you for clarifying.


I don't think that's the issue. I have a 256 GB capacity and 70 GB of free storage whenever I restart my computer. The issue is that over three days following the restart, the System Data which is normally around 68 GB starts to grow inexplicably and slowly reaches 138 GB, thus eating up all my free storage. When it has eaten up everything, I am forced to restart my computer, and I go back to the first step: 70 GB of free storage and 68 GB of System Data. Round and round.


Has anyone found a durable solution to this issue?


Thank you!

Aug 27, 2025 05:08 AM in response to Palamede

Restart your computer.


Next thing is to check Utilities->ActivityMonitor and select the Disk tab. Click on the "Bytes Written" column header to sort that column so it lists the numbers high to low. In addition, on the View menu select "Show all processes". Monitor the processes at the top periodically and note the how many writes there are with them. You will need to check periodically as the "System Data" grows.


Notes: do not restart the computer again as this will reset the data in ActivityMonitor and periodically check as the SystemData grows. If SystemData grows as fast as you state, it may only take a day to find a clear cut "offender".


Report what the results are here.


System data suddenly fills up storage and empties after restart

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