Did you try this backup function? My understanding is that the USB drive used for the backup would be directly readable by a PC computer (i.e. the backup works by copying the directories/files, not by creating some proprietary huge backup file). This is absolutely great since if the NAS fails you can continue your work immediately by connecting the backup drive to your PC via USB and accessing those files. Is my understanding correct?
No, I haven't tried it (I don't have an external USB drive). I am actually using mine for daily file backup of my PC as well as archiving of TV shows and movies that I don't care if I loose.
The backup software I am using is installed on my PC (Synology Data Replicator 3) and it backs up individual directories and files. The backup software that the NAS uses to back itself up is internal to the NAS, and I would
assume also makes individual directory and file copies.
So I believe your understanding is correct, but I can't verify for sure. Maybe a good time to test Synology support through email or forum.
Steve