Hello,
1-My main recommendation is this following guide which recommends to use for SFTP: Titan, Cygwin, OpenSsh. Make sure to use it, as it is well known to have issues when backing up.
Disaster Recovery System Administration Guide for Cisco Unity Connection Release 8.x
http://www.cisco.com/en/US/partner/docs/voice_ip_comm/connection/8x/drs_administration/guide/8xcucdrsag.html#wp42856
2- As a simple test try recreating the backup device.
3- If you have a cluster environment, and the backup only fails from the Pub but succeds on the Sub, you might be running into this bug CSCts22450 UC 8.5(1)-DRS backup of Subscriber is failing from Publisher node.
4- If the messages backup are over 1GB and you are using freeFTP you might be running into the following bug CSCsm21349 DRS Direct Backup stuck for freeFTPd server when tar size grow over 1GB.
The following thread was for UC 7.1.3 and references to this https://supportforums.cisco.com/message/3109612#31096123
There is also another bug CSCtf40892 DRS backups fail when backing up large components, but it should already be fixed for your version, in order to clarify we would need the DRF master and DRF local traces.
**As a workaround if you are not able to complete the backup for the messages with DRS and it is an urgent matter you may use the COBRAS tool : www.ciscounitytools.com\alldownloads.
Best regards,
David Peck
