I got the freeFTPd downloaded to the new server but had very hard time to get it to work. CUCM could not communicate with it. WinSCP could not connect to it either. After messing around the firewall settings, I gave it up on freeFTPd.
Then I decided to try the free version of SolarWinds SFTP/SCP server, WOW it only took me few minutes to get the backup to work.
On SFTP server, create the root directory, I also created two sub-folders to separate backup files between CUCM and UNITY.
Make sure the SFTP server is running.
On CUCM, go to Disaster Recovery System, create a new backup device.
Host name/IP address: enter the IP of the Windows server running SFTP
Path name: /CUCM (the sub-folder created in the root directory)
Username and password: same credential created in SFTP
It worked much better than the setup with FreeFTPd server based on my experience.