I'm familiar with the older CUCM release notes that freeFTPD (SFTP) couldn't write a file that was greater than 1GB. I'm betting that has been fixed as of freeFTPd 1.0.12.
In the lab I tested using freeFTPd version 1.0.12 and wrote a TAR file (SFTP) from Cisco CallManager 9.1.2SU1 that is greater than 1.0GB (it was 1.6GB) without any issue, then used Cisco DRS Restore which in 9.1.2SU1 added a File Integrity Check (SHA Message Digest) with a DRS Restore of that 1.6GB file.
Since the restore worked fine and the file integrity check validated it, I can't see any problems with Cisco recommending freeFTPd version 1.0.12.
References to problems with freeFTPd greater than 1GB
https://supportforums.cisco.com/thread/2059891
I spent some time on the freeFTPd website and can't see where they actually documented bugs or release notes of fixes in versions! Going back to 2006 their forums seems to indicate they didn't have any file size limitations.
Normally I recommend GlobalScape SFTP, good product but the licensing can cost. A free SFTP linux server is nice. In short I wish Cisco would add back plain old FTP and leave the security up to the customer. Telling customer's they need a SFTP server usually has them rolling their eyes.
