Before you start copying files to your new GMail Drive, please make sure to familiarize yourself with the Google Gmail Terms of Use. Google provides the Gmail mail service for free, so do make sure to respect their wishes for the benefit of all Gmail users.
Among other things, this means you cannot:
The GMail Drive tool is not in any way endorsed by Google. It is still considered an experimental tool. Do not copy sensitive data or rely on this tool as a secure backup solution. I cannot guarantee that files stored in this manner will be accessible in the future. You are using this tool on your own risk.