The question came up while I was thinking to move some data (e.g.) pictures, old but important other data solely to the NAS (private use, no business level).
My NAS is a simple 2 disk RAID system. I know that a RAID is not a backup system as it only provides hardware redundancy so I planned to create incremental (versioned) backups of the data directories. The backup destination would be the same NAS so that the only instance of the data (no copies on notebook or desktop machines) and the versioned backups would stay entirely on those two disks.
Now I wondered how reliable this procedure is. I've read that a power blackout has typically no effect on the data on a disk, as the heads retract to a safe position and do not "hit" or "scratch" the disks, but it can of course corrupt data currently written and even worse affect the electronics of a drive rendering it unusable.
Now I am pretty unsure whether I should invest in a small UPS that plays well with the NAS to ensure proper shutdown or resort to multiple backup locations (or both?)
Does having only one instance of data + backup on same machine still regarded unsafe?
(I am ignoring theft here. Also surges, as all connected cables LAN, Power etc. are protected. Even more: I do not want to use the cloud for any data (encrypted or not))
Edit: Sorry, it is a RAID 1 with two disks total.