Dropbox
Also known as: Dropbox storage, Dropbox online-only, Dropbox Smart Sync
Dropbox is a cloud storage service that syncs files across your devices. With Selective Sync and online-only files, items can live in the cloud without using local disk space — they download on demand when you open them.
- Online-only files use little or no local disk space
- Selective Sync controls which folders sync at all
- Local usage equals files kept offline, not the full account
Online-only vs locally synced files
A locally synced file is downloaded and takes up disk space on your device, so it opens instantly and works offline. An online-only file shows in your folder with a cloud icon but lives only in Dropbox; opening it downloads the file, and it uses little or no local space until then.
On a Mac or PC you control this with Selective Sync (which folders sync at all) and the Make available offline / Online-only options on the Dropbox desktop app. Setting big folders to online-only is the main way to keep Dropbox from filling your local drive.
How it affects disk space
The space Dropbox uses on a device equals the files it keeps locally, not your whole Dropbox account. A 500 GB Dropbox can occupy almost nothing on a laptop if most files are online-only. Conversely, marking everything "available offline" downloads full copies and can quickly fill a small drive.