I purchased a new Toshiba 1T external HD and ran reflect five or six times and all failed after running 24 hours. Then I purchased a new WD passport Ultra HD and Reflect ran successfully in 61 minutes. The backup media is important.
Unless the Toshiba drive was defected I would not expect that kind of failure on a new drive. I assume the drive was formatted with NTFS, but even if not, that wouldn't cause that kind of failure. Have you tried coping some large files to the Toshiba using Windows Explorer or similar file manager?