I know that a correct software mirror raid is subject to failures, when anything wrong is written to both disks. And I also know that hardware mirror raid is subject to hardware failures. I said at the beginning that I keep two wheezy mirror-raid servers with the same data and software. Now that mirror raid in all my machines is fully in order (also thanks to you) I maintain three wheezy servers in the same situation (I recovered what had been set aside in order to have three different jobs going on). That is multiple backup. I can switch disks from one to another one.
Very large data files are at the supercomputer center, where multiple backup is also carried out.
As to inexpensive ssh access to my machines and supercomputer center, I use a cheap tablet, equipped with a physical US keyboard, where I installed a minimal linux (ssh, text editor, browser). That allows continuous access under a negligible electricity bill.