Show me software that can mirror an SSD to HDD in realtime without the "backup" being affected by the slower write speeds. I was looking for a way to do this a few years ago, and couldn't find anything. I'd be very happy if I could pull my SSD out, change my boot drive, and boot into my existing OS without any issues. My understanding is that existing solutions for this delay write confirmation until both drives are complete, negating the speed advantage of the SSD.
Check out Syncthing. I personally run two instances of syncthing, synchronization happens very fast and as long as there isn't high write volumes it syncs pretty quickly. If you don't need realtime backup, rsync'ing in a loop would work.
