I know about all the Raids, and my idea was to use Raid6 anyway, don't mind that much about speed. I don't want to lose too much space, otherwise I will end up again with limited space. I wanted to buy this NAS and intended to use Raid6, like I already wanted to do with my Qnap, but with the Qnap I would have the problem with little space if I used Raid6. The Raid1 was never an option for me, neither was Raid0+1, exactly for the limited space reason.
It was fine so far with the Qnap and Raid5, ran perfectly for 2 years without any problems, so hopefully this one will do the same in Raid6. But one thing is for sure, if one disk would fail in the 2413+, I would switch it off, until I would have a replacement disk, otherwise I would run the risk that another one would fail ending up with losing all my data. I already wanted to order a spare disk straight away, but they're 180€, and I'm already spending 3300€, but I might want to order it anyway. But I think I should, as ordering one later if it happens might take some time.
One thing is sure, and I read that in every NAS forum, they always say to still make backups, at least for the stuff that is most important, and that's what I do, I have all my photos f.ex. backuped up on an internal disk, don't care so much about movies or series, as I could download them again, although that would be a time consuming procedure, and of course it would be a real pain, as also all my series and movies are done with Yadis and YAMJ to have the nice interface on the Mediaplayer. That was time consuming!!
I also store my music on one internal disk still, as it's quite small compared to other stuff, but I cannot have 20TB of movies and 10TB of retro stuff, and still have a backup of that, then Raid6 must be secure enough. It's still attached to my UPS, that at least protects it from power failures, so the disks are already a lot safer.
To have the real thing, you would need 2 NAS and mirror them completely, but hey, that's a lot of ca$h.