Online vs local storage: how to be sure?

Hello,

I would like to know how to be sure that my files are physically present on my local disk drive.

I selected the "Make accessible offline" (not sure about the translation, my computer being in French) setting from the context menu of the Dropbox directory. And I thought everything was ok.

But today, I wanted to copy an entire big directory from my local Dropbox folder to another machine and was surprised to see that Dropbox began to download the files form my account. Exactly as if they were not present on the local drive.

I don't think that's normal.

Hence my question: how to be sure that all my files are all really present on the local drive?

Thank you.

Patrick