Having had to rebuild another machine, After it was up and running I had a server with the OS installed on the boot disk and two spare internal disks that used to be in a raid array. While the machine supported hardware raid I chose to setup software raid as it gives me more control, and personally I would rather ‘tweak’ with the command line than at the hardware bios level.
Anyway, rather than re-create the wheel, there is a very good article at https://www.tecmint.com/create-raid1-in-linux/ that explains how to mirror up a spare two disks.
I put a LUKs filesystem on mirrored disks and made it a /home directory.
