Maybe I'll have to take another look at it when I have some free time, although I vaguely remember something not working right with the standard mdraid tools. According to this post, it seems to be a slightly customized version: https://serverfault.com/questions/568166/how-to-recover-an-m...

Thinking back on this situation made me remember the terrible thermals in that old NAS. I had to replace the (fanless) PSU 2 times because it was always blowing up and creating sparks/smoke. Lol good times.