Scan a system for RAID arrays and save findings so the array reappears across reboots:

mdadm --detail --scan >> /etc/mdadm/mdadm.conf

Create a RAID5 array out of sdm1, sdj1, and sdk1 (all partitioned with raid-autodetect partitions)

mdadm --create /dev/md1 --level=5 --raid-devices=3 /dev/sd[mjk]1