Dupe guide

Why does my Mac's storage keep filling up so fast?

If you clear 20 GB and it's gone again next week, something is silently generating files. Here's what.

4 min read

You free up 20 GB, breathe a sigh of relief, and a week later you’re back to “Your disk is almost full.” Something on your Mac is silently generating files. Here are the usual suspects and how to find which one is yours.

Suspect 1: iCloud sync

If you have iCloud Photos or iCloud Drive set to “Download Originals” / “Keep Files Here,” every new photo, document, or shared file gets pulled to your local disk automatically.

Fix:

Suspect 2: Photos imports

Every time you plug in your phone or camera, you may be re-importing photos. The Photos app deduplicates, but third-party import workflows often don’t.

Check Photos library size:

du -sh ~/Pictures/Photos\ Library.photoslibrary

If it’s growing faster than expected, Optimize Mac Storage is your friend.

Suspect 3: Time Machine local snapshots

macOS takes hourly local snapshots when your Time Machine drive isn’t connected. They auto-purge when space is needed, but until then they count as used space.

tmutil listlocalsnapshots /

Each snapshot is typically 5–20 GB. Just keep using your Mac and macOS will manage them.

Suspect 4: Xcode

If you compile anything with Xcode (or any toolchain that uses derived data):

du -sh ~/Library/Developer/Xcode/DerivedData
du -sh ~/Library/Developer/Xcode/iOS\ DeviceSupport

DerivedData can grow by 1–5 GB per project per week. Safe to clear:

rm -rf ~/Library/Developer/Xcode/DerivedData/*

Suspect 5: Docker and VMs

Docker keeps a single disk image that grows monotonically:

du -sh ~/Library/Containers/com.docker.docker/Data/vms/

Reset it via Docker Desktop > Preferences > Resources > “Disk image size.”

VMware/Parallels/UTM disk images live in /Documents or /Virtual Machines and grow as the VM uses space.

Suspect 6: Mail attachments

Every email you open with an attachment caches it locally:

du -sh ~/Library/Containers/com.apple.mail/Data/Library/Mail\ Downloads/

Fix: Mail > Settings > Accounts > Advanced > “Download Attachments: None” or “Recent.”

Suspect 7: Logs and analytics

Niche but possible. Some apps write verbose logs:

du -sh ~/Library/Logs/* 2>/dev/null | sort -h | tail -10

Suspect 8: Duplicates accumulating

This is the silent one. Every photo you import twice. Every PDF you save to Downloads and then move to Documents. Every project you copy. Each is small, but they compound. Over a year you can accumulate 5–15 GB of pure duplication.

Download Dupe for a periodic sweep. It SHA-256 hashes every file, finds byte-identical duplicates, and moves them to the Trash. Run it once a month and you’ll see exactly which workflow is generating dupes. $14.99 once, never permanent deletes, never touches system files.

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