Mac System Data Exceeding 200GB? Here’s How to Actually Clear It

— A Deep Dive with Heavy Keynote Usage and Time Machine as Examples

I. Problem Overview

After long-term use, some macOS users discover that “System Data” in Storage Settings grows abnormally large. Common symptoms include:

System Data occupying 200GB or more

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No corresponding files can be located in Finder

Deleting caches or log files has little effect

Third-party cleaning tools are ineffective

Uninstalling and reinstalling apps (such as Keynote) does not help

Even after reinstalling macOS, the issue reappears after some time

This problem is especially common among heavy productivity users, such as those working extensively with Keynote, Final Cut Pro, or design tools.

II. Commonly Tried but Ineffective Solutions

Users typically attempt the following methods, most of which fail to solve the problem at its root:

Manually deleting directories such as ~/Library/Caches and ~/Library/Logs

Using third-party cleaning tools like CleanMyMac or similar utilities

Uninstalling and reinstalling Keynote

Reinstalling macOS via “Reinstall macOS”

These approaches are limited because they do not address the real sources behind System Data inflation.

III. What Exactly Is “System Data”?

It is important to understand that:

System Data is not a real folder, but rather a collection of data that macOS cannot accurately categorize.

System Data may include, but is not limited to:

macOS system temporary files

Application and system caches

Portions of the user Library (~/Library)

Files Spotlight cannot classify

Large resource files inside application packages

Local caches from cloud services (such as iCloud or OneDrive)

iPhone / iPad backup files

Residual data from deleted user accounts

Time Machine local snapshots

As a result, System Data cannot be reliably inspected or reduced through simple cache deletion or Finder-based browsing.

IV. Key Cause #1: Time Machine Local Snapshots Consuming Disk Space How Local Snapshots Work

Even when no external drive or NAS is connected, macOS will:

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Create a Time Machine local snapshot every hour

Retain snapshots from the last 24 hours by default

If the backup destination remains disconnected, keep local snapshots associated with the most recent full backup

These snapshots:

Are based on the APFS file system

Do not appear as regular files

Are entirely counted under System Data

In some cases, local snapshots can consume tens or even hundreds of gigabytes.

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Why They Sometimes Cannot Be Deleted

When Time Machine uses a NAS or network storage device as its backup destination, the following situations may occur:

The NAS was previously disconnected

The network path or IP address changed

The backup was not re-“claimed” by the system

As a result, macOS may treat these snapshots as belonging to an unreachable backup destination, leading to:

tmutil deletion failures

Errors such as Stale NFS file handle

Snapshots that cannot be reclaimed, causing persistent disk usage

V. Key Cause #2: How Keynote and Similar Apps Amplify System Data

Keynote itself is not malfunctioning, but its design inherently amplifies System Data usage:

Keynote files are actually packages containing large numbers of resources

These may include:

High-resolution images

Embedded videos

Fonts

Animation and transition assets

Spotlight sometimes fails to correctly classify these resources, causing them to be grouped under System Data.

For users who frequently create large, media-heavy presentations, steady growth in System Data over time is expected.

VI. Effective Solutions (Prioritized) Solution 1: Verify and Restore Time Machine Backup Status (Recommended)

Open Disk Utility

From the menu bar, select Show APFS Snapshots

Select the system Data volume

Check whether a large number of Time Machine local snapshots exist

If using a NAS as the backup destination:

Reconnect the NAS

Select the original backup in Time Machine settings

Follow the prompts to claim the existing backup

Once the backup relationship is properly restored, macOS can automatically manage and reclaim snapshot space.

Solution 2: Use Disk Analysis Tools to Identify Real Space Usage

It is recommended to use tools that analyze disk usage without automatically deleting files, such as:

GrandPerspective

EtreCheck

The goal is to identify:

Which files or directories consume the most space

Whether disk usage is abnormally concentrated in specific areas

Avoid relying on “one-click cleanup” tools.

Solution 3: Check for Residual Data from Old User Accounts

If the device previously:

Had multiple user accounts

Removed accounts without deleting their home folders

Then old home directories may still exist and be counted as System Data.

Solution 4: Rebuild the System Environment Completely (Last Resort)

When System Data usage becomes severely unmanageable and no clear source can be identified, the only definitive solution is:

Fully back up all current data

Erase the disk and reinstall macOS

During setup:

Migrate only the user account

Do not migrate system settings, applications, or Library data

This approach completely removes legacy data structure issues.

VII. Long-Term Prevention Tips (for Keynote and Content Creators)

Archive older Keynote projects to an external drive or NAS

Avoid storing large volumes of presentation files locally for long periods

Keep the Time Machine backup destination consistently available

Avoid third-party tools that perform automated “system-level cleaning”

Periodically monitor disk usage with analysis tools

VIII. Conclusion

Abnormally large macOS System Data usage is rarely caused by a single cache or log issue. Instead, it is typically the result of Time Machine local snapshots, application package resources, and inherited historical data structures working together.

Only by understanding what System Data actually contains—and addressing the root causes—can disk space issues be resolved effectively and long-term.