--- title: "Mac System Data over 100 GB? Why, and how to fix it" description: "System Data at 100–500 GB is common on Sequoia, Tahoe and macOS 27. The five usual causes, how to tell which one it is, and how to fix it safely." url: https://tidymac.space/guides/mac-system-data-100gb/ updated: 2026-10-16 --- [Home](/) [Guides](/guides/) Mac System Data over 100 GB? Why, and how to fix it # System Data is over 100 GB on my Mac: what’s using it? System Data at 100–500 GB is common on Sequoia, Tahoe and macOS 27. The five usual causes, how to tell which one it is, and how to fix it safely. 8 min readUpdated October 16, 2026By the Tidy Mac team Short answer When System Data passes 100 GB, it is almost always one of five things: Time Machine local snapshots, iPhone or iPad backups, app caches and app data, developer files (Xcode, Docker, AI models), or a runaway system cache. Find which one is big first, then remove only that; never delete System Data blindly. The steps 1. Restart your Mac; macOS clears swap and some temporary files on its own. 2. Check Time Machine local snapshots with tmutil listlocalsnapshots / and thin them. 3. Open Finder › your device › Manage Backups and remove backups you no longer need. 4. Check ~/Library/Caches and ~/Library/Developer for the biggest folders. 5. Look for large AI models (Ollama, LM Studio, Hugging Face) and Docker disk images. 6. Check for a runaway system cache such as com.apple.mediaanalysisd. ## The five usual causes, biggest first 1. **Time Machine local snapshots.** Hourly restore points kept on your own drive. They can hold 20–150 GB and are counted as System Data. [What they are](/learn/time-machine-local-snapshots/) 2. **iPhone and iPad backups** made with Finder: 10–100 GB each. [Where they live](/learn/iphone-backups-on-mac/) 3. **App caches and app data** in ~/Library. [App caches explained](/learn/mac-app-caches/) 4. **Developer and AI files**: Xcode DerivedData and simulators, Docker’s disk image, Ollama and LM Studio models (each model is 2–40 GB). [For developers](/for/developers/) 5. **A runaway system cache**, for example [com.apple.mediaanalysisd](/folders/com-apple-mediaanalysisd/) on some macOS versions. ## Find which one it is (2 minutes) In Terminal: ``` tmutil listlocalsnapshots / du -sh ~/Library/* 2>/dev/null | sort -h | tail -15 ``` The first command lists snapshots. The second shows your 15 biggest Library folders. Or paste the output into the free [System Data explainer](/tools/system-data-explainer/), which labels each folder in plain English, in your browser. ![](/img/brand/tidy-128.png) ### Let Tidy Mac do this for you See every part of your storage explained, and clear junk to the Trash with Undo. $9.99 once, 2 Macs. [Download](/download/TidyMac.dmg) [Buy for $9.99 once](/buy/) ## Fix only the big part - **Snapshots:** `sudo tmutil thinlocalsnapshots / 999999999999 4` (your external Time Machine backups are not touched). - **Device backups:** Finder › select the device › Manage Backups › delete old ones. - **Caches:** quit the app, then move its folder in ~/Library/Caches to the Trash. - **Developer files:** use each tool’s own command (Xcode › Settings › Locations, `xcrun simctl delete unavailable`, `docker system prune`, `ollama rm`). ## Why it comes back Snapshots, caches and backups all grow again by design. Checking once a month, or letting Tidy Mac notify you when your disk is almost full or used space jumps, keeps System Data from creeping back to 100 GB. ## Keep reading [What is “System Data” on a Mac, and why is it so big?](/learn/what-is-system-data-on-mac/)[How to clear System Data on macOS 27 Golden Gate without breaking anything](/guides/clear-system-data-macos-27/)[Time Machine local snapshots on Mac](/learn/time-machine-local-snapshots/)[System Data explainer](/tools/system-data-explainer/)[My Mac says storage is full, but I can’t find any files](/guides/mac-storage-full-but-no-files/)[Why System Data keeps growing (and how to stop it)](/guides/mac-system-data-keeps-growing/) Share:[X](https://x.com/intent/post?text=System%20Data%20is%20over%20100%20GB%20on%20my%20Mac%3A%20what%E2%80%99s%20using%20it%3F&url=https%3A%2F%2Ftidymac.space%2Fguides%2Fmac-system-data-100gb%2F)[Reddit](https://www.reddit.com/submit?url=https%3A%2F%2Ftidymac.space%2Fguides%2Fmac-system-data-100gb%2F&title=System%20Data%20is%20over%20100%20GB%20on%20my%20Mac%3A%20what%E2%80%99s%20using%20it%3F)[Hacker News](https://news.ycombinator.com/submitlink?u=https%3A%2F%2Ftidymac.space%2Fguides%2Fmac-system-data-100gb%2F&t=System%20Data%20is%20over%20100%20GB%20on%20my%20Mac%3A%20what%E2%80%99s%20using%20it%3F)[LinkedIn](https://www.linkedin.com/sharing/share-offsite/?url=https%3A%2F%2Ftidymac.space%2Fguides%2Fmac-system-data-100gb%2F) #### On this page [The five usual causes, biggest first](#the-five-usual-causes-biggest-first)[Find which one it is (2 minutes)](#find-which-one-it-is-2-minutes)[Fix only the big part](#fix-only-the-big-part)[Why it comes back](#why-it-comes-back) **Tidy Mac** See this on your own Mac in under a minute. $9.99 once, 2 Macs. 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