@Dont-Worry the apps run as containers and each container has it's own file system (completely different from the host filesysted). It is a sort of sandboxing for security.
What this setup means is that, even if your disc is attached to the machine, the app containers won't see it! It will be available on the host ubuntu itself but not to the apps. Cloudron Volumes is a mechanism to expose these discs on host to the apps. Hope that clarifies!
But if I could use it as a classic disc, I should mount it as a Cloudron volume If I understood correctly.
Right, and there is no way around not creating a volume.