As others have said, you should really be careful treating your RAID as a backup. I for one do all of my backing up on Playstation 1 memory cards… I had to buy a couple storage containers to store them all, but I guess that technically counts as off-site

My Synology NAS was running for 6+ years before I replaced it last year. And the only reason I replaced it was to upgrade the hardware to be able to act more like a home server running some more demanding services.

I’ve since given the NAS away to a friend who is still running it… As always back up your data just in case, but I wouldn’t expect the hardware to crap out on you too soon