Even better: Raid 6, with hot spare, cold spare on the shelf, and a unit that supports regular self-consitancy checking and automatic failure notification. My primary nas even has a wireable relay trigger, which is hooked to turn on a $20 spinning red light (old cop car style) sitting on top of the cabinet when there's an alert.
It's also powered by two ups's (one for each power supply) and supports network controlled shutdown on both.
If you can, order the drive packs (we got 2 packs of 4) from different vendors to minimize the chance of getting the same 'lot' of drives. Look at the amount of storage you need and get the minimum size drives... because they rebuild faster you are at less risk of a multi failure. I'd much rather have 12x 1 TB drives than 4x 3TB drives.
(And if you scoff at Raid 6, I've had a second drive fail hard during the rebuild when the system detected a probable failure on a drive and started to rebuild with the hot spare at 3 am...)
Also, backup backup backup.
If you need speed of course, you want raid 1+0. That's fine, my rule of thumb is:
Start with one hot spare, one cold spare.
After each 3rd mirror pair, add another hot spare. (so 6 total in use drives needs 2 hot spares)
Add another cold spare after every other hot spare.
Cold spares should be testable and tested. I will swap them out with the hot spares once a month.
But I'm paranoid.
Also:
Backup Backup Backup. RINB.
Also: HARDWARE RAID CARDS.
I can't stress that enough. software and semi-software raid is a joke.