I want to build a proper server with room for 40+ HDDs to move my media server to and have RAID 1. I know a lot about PCs and software, but when it comes to server hardware I have no clue what I'm doing. How would I go about building a server that has access to 40+ RAID 1'd HDDs?
The chance of a rebuild taking longer than a failure occurring is non zero. RAID 1 is less protection that raid 50 or raid 60, plus depending on how many disks you have you will save space and get better performance.
But you need a good controller.
I'll have to watch a video later I guess. I know it's possible to lose a drive while it's rebuilding, but it's improbable, and I figured it takes more space, I'm okay taking that risk since I'm not handling irreplaceable data, just my personal TV/movie archive for now. But if it can save space, I'll have to consider it.
It is far less improbable than you think, especially if all of your drives have similar age/wear - as would be the case if you bought all 40 around the same time.