title: Truly virtual FTP
body: <p>I am looking to set up an FTP server without connecting it to a file system.</p>
  
  <p>I want to use a database to store which of the many large files on my site each user will have access to. Because of the number and size of the files involved, the files cannot all be stored on a single server so a link based setup is not useful.</p>
  
  <p>I am imagining an FTP server that will act as a pass-through for a backend CDN that stores all the files and checks a remote database for which files to present.</p>
  
  <p>Does a system like this exist? If it doesn't exist, Which open source FTP server would be easiest to modify to suit my needs?</p>