Your cloud backup app keeps its own cache on the Mac it is backing up
Online backup apps keep indexes, caches and sometimes local copies. How big they get, where they are, and which are safe to leave alone.
A backup app that sends your files to the cloud needs to remember what it has already sent. It keeps an index of every file, and often a cache to speed up uploads. On a Mac with hundreds of thousands of files, that bookkeeping can be several GB.
Common locations
du -sh /Library/Backblaze.bzpkg/bzdata 2>/dev/null
find /Library ~/Library -maxdepth 3 \( -iname '*arq*' -o -iname '*crashplan*' -o -iname '*idrive*' -o -iname '*carbonite*' \) -exec du -sh {} + 2>/dev/nullWhat to do about it
| You see | Do |
|---|---|
| A few hundred MB to a few GB | Leave it. It is how the app knows what is backed up |
| Many GB and growing fast | Check the app's settings for cache size, or contact its support |
| An app you no longer use | Uninstall it properly with its own uninstaller |
Local snapshots from backup apps
Some local backup tools, and Time Machine, keep snapshots on the source disk. Those hold deleted files' space. See deleted files but storage not freed.
Comparing backup approaches: Carbon Copy Cloner versus Time Machine.
Common questions
Why does my backup app use space on my Mac?
It keeps an index of every file and often a cache to speed up uploads. On a large Mac, that can be several GB.
Can I delete Backblaze's bzdata folder?
Not by hand. It holds the record of what has been backed up. Deleting it can trigger a full re-upload. Use the app's own options or uninstaller.
Do backup apps keep copies of my files locally?
Most keep only an index and cache. Some local tools and Time Machine keep snapshots on the disk, which hold space until removed.