It doesn't really matter how much you try to build redundant arrays your best option is to always use a full backup service. Redundancy just helps you keep your files intact locally so you can use them in the meanwhile after one hdd failure but a remote backup (like to a backup-specializing company) is generally the better option (generally once one drive has failed you're likely to replace all the drives of the same model or at least the ones you bought in the same batch). Once you start hear clicking it'll probably be too late to try to manually copy all of the files off of it.
http://www.smallnetbuilder.com/nas/nas-features/31745-data-recovery-tales-raid-is-not-backup
It's the laziest solution but it's probably the most effective. Unless you really want that data to stay out of the hands of people who do backups or anywhere on the internet (even though the machine is connected to the internet even if it's LAN storage) or are a file storage/backup holder yourself you really shouldn't have to think about it. Most of us are better off spending the money every year on a backup service instead of having to spend a ton of extra cash, time, and obtaining the needed knowledge with setting up our own servers/redundant storage and worrying about having to maintain it. For some people it's a hobby, more the rest of us it's a nuisance.
Although don't take this as a reason to RAID 0 everything so long as you have backups. I'm not sure how backup programs are right now (if they do snapshots every set amount of time or if they sync individual file changes now like cloud storage software like in Box or Dropbox) so make sure you check up on the backup/update method.
**Not saying RAID is useless. Using it in a NAS or desktop does give you performance benefits (honestly we really only care about the benefits in performance it gives to HDDs. SSDs, unless you need that much speed, won't make much of a difference) as long as it isn't RAID 1. RAID 0 and no RAID at all are the most space efficient and all of the other ones are less space efficient. I'd actually advocate for RAID 0 if we're talking about hard drive lifespan because it's essentially wear-leveling like how the NAND chips in SSDs are treated (you can think of all of the NAND chips on that board in a big RAID 0 array but with really low failure because it's solid state). RAID 1 is kind of silly because if you're using the same drive from the same batch (most likely if you planned on doing a RAID 1 array prior to purchase you went for 2 of the same drive on the same order) you're basically just killing 2 drives at the same rate at the same time (which have the same lifespan).
