In order to set up software raid we need to install mdadm tools (Ubuntu/Debian)
apt-get install mdadm
Now for setting up raid one using two drives for example /dev/sdd and /dev/sdc we are issuing the following command
mdadm --create /dev/md2 --level=1 --raid-devices=2 /dev/sdc /dev/sdd
mkfs.ext4 /dev/md2