This setup installs Debian Buster on twin drives (which do not need to be identical) in RAID 1 mirror mode.
Two partitions are created, one for swap and the other for data using the “news” inode allocation scheme.
Blanking the drives is optional but useful for reinstall.
Boot from USB media, debian xfce live CD
https://cdimage.debian.org/debian-cd/current-live/amd64/iso-hybrid/debian-live-10.2.0-amd64-xfce.iso
sudo -s
dd if=/dev/zero of=/dev/sda bs=4M
dd if=/dev/zero of=/dev/sdb bs=4M
dd if=/dev/zero of=/dev/sda bs=4M count=1
dd if=/dev/zero of=/dev/sdb bs=4M count=1
Boot from USB media, debian net install
https://cdimage.debian.org/debian-cd/current/amd64/iso-cd/debian-10.2.0-amd64-netinst.iso
We setup the two discs as independent clones of each other then add both as RAID 1 as two partitions, one for data and the other as swap.
If the machine does not boot after install, change the drive order in the BIOS and reboot.
Login as root
/bin/su - root export PATH=/bin:/sbin:/usr/bin:/usr/sbin
Install grub onto second drive.
grub-install /dev/sdb
Install useful software.
apt-get install apt-file smartmontools sudo vim tcsh bc build-essential git mercurial apt-file update update-alternatives --set editor /usr/bin/vim.basic