Pardon what might come across as a stupid question. I have a number of backup disks on my system, and I'm transitioning to SSDs. Now, it is pretty clear that per unit storage, USB flash drives are a lot cheaper than SSD drives. But I've been (sort of casually) warned against using USB flash drives for backup. So my question is, why are SSD drives worth it, for doing backups, compared with USB flash drives? Is it speed? Is it reliability? Is it lifetime? Why do people even bother getting full up SSD drives (e.g. SATA),instead of USB flash drives for storage? My understanding is that the basic storage architecture is the same. A pointer to explanatory details would be helpful.