# How to reduce System Data on a Mac > What System Data is in Mac storage, why it grows to tens of gigabytes, and six safe ways to shrink it without breaking macOS. - URL: https://maccleaner.tech/reduce-system-data-mac/ - Published by: Mac Cleaner Guide, written by the Bytesweep team (Bytesweep is the publisher's own app) - Last updated: November 12, 2026 - Steps checked against Apple's documentation for macOS 27 in November 2026. System Data is everything macOS cannot file under Apps, Documents, Photos or another named category. To reduce it, clear app caches and logs, delete old iPhone backups, and look inside your Library folder for large app data. macOS manages the category itself, so Storage settings shows its size but will not let you open it. Do not delete anything in `/System`. ## What System Data is In **System Settings > General > Storage**, the gray System Data block is a leftover category. Apple describes it as files and data used by the system, such as log files, caches and virtual memory files. In practice it also takes in app support files, virtual machine and container disk images, fonts and plug-ins. Older versions of macOS called it "Other". Unlike the other categories, it has no info button: macOS lists it by size only. Apple publishes no normal figure. In our experience 15 to 30 GB is common on a Mac used for everyday work. When it reaches 80 or 100 GB, one or two specific things are usually responsible, and finding them is the whole job. ## 1. Remove local Time Machine snapshots If you use Time Machine, macOS keeps local snapshots on the internal disk for about 24 hours. Apple counts the space they use as available, and deletes them as they age or when space is needed, so they are rarely the real cause of a full disk. They can still make the numbers confusing. List them in Terminal: ``` tmutil listlocalsnapshots / ``` Delete one by its date stamp: ``` tmutil deletelocalsnapshots 2026-11-10-093012 ``` Because macOS removes these by itself, deleting them by hand only helps when an installer or another tool insists there is not enough room right now. ## 2. Find the large folders in your Library Most oversized System Data lives in your user Library. In Finder, choose **Go > Go to Folder** and enter `~/Library`. Or let Terminal rank the folders by size: ``` du -sh ~/Library/* 2>/dev/null | sort -h | tail -15 ``` The usual suspects are `Caches`, `Application Support`, `Containers`, `Group Containers` and `Developer`. Open the biggest and look for apps you recognize. ## 3. Clear caches and logs Quit your apps, then empty the contents of `~/Library/Caches` and `~/Library/Logs`. Delete what is inside the folders, not the folders themselves. Apps rebuild what they need. Full steps are in our guide to [clearing the cache on a Mac](https://maccleaner.tech/clear-cache-mac/). ## 4. Delete old iPhone and iPad backups Backups made through Finder sit in `~/Library/Application Support/MobileSync/Backup` and can run to tens of gigabytes each. Remove them from **System Settings > General > Storage > iOS files**, or in Finder with the device connected, under **Manage Backups**. ## 5. Check developer tools and virtual machines If you write software, this is often the whole answer. Xcode's `~/Library/Developer` folder (DerivedData, simulators, device support), Docker's disk image, and virtual machines from UTM, Parallels or VMware all count as System Data and each can exceed 50 GB. Clean them from inside the tool that made them where you can; deleting a VM's disk file by hand deletes the machine. ## 6. Restart A restart clears the swap file and temporary files and lets macOS recalculate the storage figures. If System Data dropped after a restart, the growth was temporary. ## What not to delete - Anything under `/System`. It is sealed and macOS needs it. - The swap files in `/System/Volumes/VM` (`/private/var/vm` on older systems). macOS creates and removes them itself. - Whole folders in `~/Library/Application Support` for apps you still use. That is where apps keep your data, not just leftovers. **The faster way, with our own app.** Bytesweep has a System Data page that lists what the gray block is made of, item by item, with sizes and a plain description of each. This site is published by the Bytesweep team, so read that as a recommendation from the maker. It is free to try for 3 days, which is enough to see the breakdown; cleaning needs the USD 29.99 one-time license. [See how it shows System Data](https://bytesweep.app/mac-system-data.html). ## Why the number keeps changing System Data moves because caches, swap and temporary files are created and discarded all day. A swing of several gigabytes between morning and evening is normal. Worry about the trend over weeks, not the figure on one afternoon. For the wider picture, see [how to free up space on a Mac](https://maccleaner.tech/free-up-space-mac/). ## Quick answers ### What is System Data on a Mac? The storage category for files macOS manages itself and cannot file under a named category: caches, logs, virtual memory files, app support files and virtual machine disk images. ### How much System Data is normal on a Mac? Apple publishes no figure. In our experience 15 to 30 GB is common; 80 GB or more usually comes from one or two specific things, such as developer tools, virtual machines or one app's cache. ### Is it safe to delete System Data? Parts of it. Caches, logs and old iPhone backups are safe to remove. Never delete anything under /System, which includes the swap files in /System/Volumes/VM. ## Sources - [Apple Support: Free up storage space on Mac](https://support.apple.com/en-us/102624) - [Mac User Guide: Change Storage settings on Mac](https://support.apple.com/guide/mac-help/change-storage-settings-mchl3d437fbc/mac) - [Apple Support: About Time Machine local snapshots](https://support.apple.com/en-us/102154) - [Apple Support: Locate and manage backups of your iPhone or iPad](https://support.apple.com/en-us/108809) - [Mac User Guide: Optimize storage space on your Mac](https://support.apple.com/guide/mac-help/optimize-storage-space-sysp4ee93ca4/mac)