Are files uploaded directly to remote servers?

The files are initially stored in container specified as the intial container in the class.

If the intial container is not actually present in the class then the files will be deleted from the initial container once they have been successfully propagated to all containers that are in the class.

It definitely yes when you use cloud storage or FTP.

Recently, I found it's wrong.

Although I'm using FTP for initial container, it seems still will upload to local directory first.

The directory shows like this just after saving node.

After refresh the page, it turns to.

URLs that take the form system/storage/serve/ are actually generator URLs - the file does not exist yet.

You mean it's just some binary in temp or cache?

no - the file doesn't exist yet so there can't be a url that points to it. the generator url creates the file in the initial container of the class and then issues an http redirect to the file.