Do you want to backup for future purposes with Tablo? Or to make sure you have the video files for offline use or use on other devices? If it is the latter, then check out this:
It works great for me to rip off of the Tablo to my Plex server. The best thing is you don’t have to disconnect it or disturb the Tablo at all. I also run it through MCEBuddy to remove commercials for movies that I keep.