macOS system data oversized

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Level 1

10 points

macOS system data oversized

Hi, I run MacOS 26.1 on an Macbook Air M3 with 16gb and 512Gb. My system data allocation size seems abnormally big (220+ Gb). From a cloud perspective, i have 2Tb cloud storage, along with microsoft365 1tb OneDrive on which i backup my files with Carbon Copy. It looks like OneDrive is the one taking all the space on my Mac. The minute i backed up the one drive files locally and deleted them on Onedrive, my system data size went back down to normal size. Can someone explain if this is a coincidence or is Onedrive and iCloud are not to live together in macOS.

MacBook Air 13″, macOS 26.1

Posted on Nov 10, 2025 3:26 PM

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Answer 1

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iamshivam

Level 2

176 points

Nov 10, 2025 11:17 PM in response to Pdupontp

What’s happening is OneDrive caches and placeholder files are stored deep inside your ~/Library/CloudStorage and ~/Library/Application Support folders, and macOS classifies those under System Data, not Documents.

When you synced or backed up OneDrive locally, macOS indexed all those files and temporarily duplicated metadata, inflating System Data. Once you removed the local copies, it recalculated and shrank back. iCloud and OneDrive can coexist just fine, but having both sync large datasets locally often causes this kind of bloat.

The fix is to keep OneDrive in “Files On-Demand” mode so it doesn’t mirror everything on disk, that keeps System Data clean and your SSD have breathing space.

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Answer 2

Nov 10, 2025 7:07 PM in response to Pdupontp

Generally regarding System Data, see this User Tip:

How to free up ‘System Data’ and other st… - Apple Community

You can certainly have OneDrive and iCloud Drive running on the same Mac, I do. There is an option to store OneDrive files locally, in which case they'll take up space on your drive. I don't keep enough on OneDirve to matter for my 2 TB internal drive, but given their storage location (several folders deep in the ~/Library folder), macOS/Spotlight will include them in System Data.

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