How on-demand sync works in the Proton Drive Windows app
Proton Drive’s on-demand sync feature lets you access all your cloud files directly from File Explorer without taking up unnecessary space on your hard drive. This article explains how on-demand sync works on Windows and how to control which files are stored locally.
Note: You must have the Proton Drive Windows app installed on your device to follow these instructions.
How does on-demand sync work in Proton Drive?
Once you install the Proton Drive Windows app and sign in, your cloud files are mirrored in a local Proton Drive folder.
Here’s how it works:
- Files and folders that only exist in the cloud appear in your File Explorer as placeholders — only their metadata and thumbnails are displayed.
- When you interact with a cloud-only file (such as opening or copying it), Proton Drive will automatically download it to your device.
- You can manually manage a file’s availability by right-clicking it in File Explorer and selecting Free up space, Always keep on this device, or adjusting the options to make it temporarily available offline.
- When you enable the Optimize storage option in the Proton Drive app, files in the selected folders become temporarily available offline. Turning off this setting will make those files permanently available offline.
How to recognize the sync status on Windows
You can recognize a file’s sync status by the small icon overlay in File Explorer and by the detailed description shown in the status bar:
Available when online
By default, files synced from the cloud appear as online-only (cloud-only), with the Available when online status. These files take up no local storage and are marked with a 
You need an internet connection to open online-only files. Proton Drive will automatically download the file when you access it, changing its status to Available on this device.
You can also make a file permanently available offline by right-clicking it and selecting Always keep on this device.
If you later deselect Always available on this device, the sync status will change to Available on this device.
Available on this device
Once you open an online-only file, it’s downloaded and saved locally. Its status changes to Available on this device, indicated by a 
Files you copy from your device into the local Proton Drive folder are Available on this device by default. You can also set this status by right-clicking a file, unchecking Always keep on this device, and not selecting Free up space.
Unlike files with the Always available on this device status, those marked as Available on this device may be removed automatically by Windows when you’re running low on disk space — depending on your Storage Sense settings(neues Fenster).
To make a file cloud-only again and free up disk space, right-click it and select Free up space.
Always available on this device
To permanently keep specific files or folders offline, right-click them and choose Always keep on this device.
These items are marked by a
icon and, unlike files with the Available on this device status, they won’t be removed automatically — even if you’re low on storage.
Regardless of a file’s availability status, any edits you make are synced to the cloud. For example, if you’re offline and edit a file marked Available on this device or Always available on this device, your changes will be automatically uploaded once your internet connection is restored.