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MacBook Air storage unexpectedly full due to macOS and System Data

On Saturday I logged on to my MacBook Air to copy some files from a memory card into my iCloud Drive. I was surprised to be told that I couldn’t do it because my hard drive was full. I deleted four large apps, freeing up around 8gb of space, and was thus allowed to copy the files.


On Sunday I logged on again to check my bank statements and was astonished to be told, again, that my drive was full. Clearly I’d not used the MacBook since the previous day, and can’t understand what has filled up all that memory.


Assuming that I can share the screenshot ok, the only area with sufficient storage use is MacOS and System Data and I certainly don’t understand how either of those would have increased by 8gb overnight, when I was not using the MacBook.


Any advice please?

1 reply

To be rid of the continual warnings, you'll need to free up as much storage as you can. MacOS likes to have a minimum of about 50 GB of free space at all times. This give the OS room to copy, download, expand and work with files properly without complaining.


A good rule of thumb is to always have at least 10%-15% of the drive capacity available at all times. For a 500 GB drive that's 50-75 GB. For a 250 GB drive, that's 25 GB and that's barely enough to keep the problem away.


You can move some of the files from your startup drive to an external drive to free up space.


You can also install the OS on a higher capacity external drive and use that as your startup disk to avoid the problem.


This from Apple on the subject of freeing up space:

Free up storage space on Mac - Apple Support

Find and delete files on your Mac - Apple Support