Zotero storage full? The 300 MB warning does not mean your library is full
The free 300 MB quota is for attachment files uploaded to Zotero's servers. It does not limit how many references you can keep locally, and it does not mean Zotero is about to stop storing your local library.
What happens when you reach the quota?
Your local Zotero library can be much larger than 300 MB. When the online file quota is full, new attachment files cannot finish uploading to Zotero Storage, so those files may not be available on your other devices through Zotero's file sync.
Zotero's library-data syncing is separate from attachment-file syncing. The warning is therefore a file-sync problem, not a limit on your references, notes, or collections.
Four safe options
1. Check whether old files can actually be removed
If you no longer need some attachments, delete them deliberately, empty Zotero's trash, and sync. Be aware that a library with several gigabytes stored locally can immediately fill a small online tier again as previously unsynced attachments begin uploading.
2. Upgrade Zotero Storage
This is the simplest supported option and is required for syncing attachment files in Zotero group libraries. Zotero currently publishes 2 GB, 6 GB, and unlimited individual storage tiers in addition to the free 300 MB allowance.
3. Use WebDAV for personal-library attachments
Zotero supports third-party WebDAV servers for attachment files in My Library. Your Zotero account continues to sync the library data; WebDAV becomes the location used for the personal attachment files.
Refory provides 50 GB of hosted WebDAV storage, free during beta, so you can use Zotero's built-in WebDAV option without running your own server.
4. Use linked files when their limitations fit
Advanced users can keep files outside Zotero's managed attachment storage and link to them instead. This can work well for specific desktop workflows, but it is a different model from Zotero's normal stored-file syncing and has device and web-library limitations. Do not choose it only because the quota warning feels urgent.
Avoid the dangerous shortcut
Do not put Zotero's data directory in Dropbox, Google Drive, OneDrive, or a similar cloud-sync folder. Zotero warns that this can corrupt its database. If you want third-party cloud storage, use supported WebDAV file syncing or a carefully designed linked-file workflow instead.
Which option should you choose?
| Your situation | Best starting point |
|---|---|
| You use group-library attachments | Zotero Storage |
| You want the simplest first-party experience | Zotero Storage |
| Your large personal PDF library needs more synced space | Hosted WebDAV such as Refory |
| You already run reliable WebDAV infrastructure | Your own WebDAV server |
| You intentionally manage external files yourself | Linked files |
References: Zotero's quota explanation and cloud data-directory warning.