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macOS Internals•6 min read•Aug 08, 2026

How to Fix Huge "System Data" (Other Storage) on macOS Sequoia & Sonoma

Elena Rostova
Principal macOS Engineer

Quick answer

System Data is mostly caches, logs, Time Machine local snapshots, iPhone backups and developer files. List snapshots with `tmutil listlocalsnapshots /` and delete old ones, clear ~/Library/Caches, remove old device backups in Finder, and clean Xcode or Docker data if you develop — then restart so macOS recalculates the number.

Table of Contents

1. What Actually is macOS System Data?

In macOS System Settings > General > Storage, "System Data" (previously named "Other") is a catch-all category for files that do not fall into Applications, Documents, Photos, or Developer categories.

2. APFS Time Machine Local Snapshots

If Time Machine is enabled, macOS creates local APFS read-only snapshots every hour whenever your backup disk is disconnected. These snapshots freeze deleted files on your drive, preventing disk space from being reclaimed.

# List local APFS snapshots
tmutil listlocalsnapshots /

# Delete local snapshots to reclaim space
tmutil deletelocalsnapshots /

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