Uh, data stored on one drive will only be on one drive. If that drive dies, you won't be able to access anything using the secondary one.
Do you just want to have a local backup drive? In which case I can recommend partitioning your secondary drive into a mirror. Having a second OS on it would be mostly pointless.
The best system I've found is to have a separate storage device dedicated to only the OS and dependant applications. So I've got a 240gb Nvme with the OS (drive C), and then another drive that has stuff I use on it.
A drive is like a box. If you break that box, it's gone, along with everything inside it. So I wouldn't recommend having your OS on the same drive as other stuff. Having Win7 on another drive won't let you access anything on another of the drives if it dies.
You can make a virtual machine if you want a second OS that has access to everything, but your problem will remain.
So basically, having a mirrored drive is the best you can do, but you'll cleave your available storage space in half.