Create array

mdadm --create /dev/mdX --level=X --raid-devices=X /dev/sdX /dev/sdY

Delete array

mdadm --stop /dev/mdX
mdadm --zero-superblock /dev/sdX
mdadm --zero-superblock /dev/sdY

Add disk to array

mdadm /dev/mdX --add /dev/sdX

Set disk as faulty

mdadm /dev/mdX --fail /dev/sdX

Remove disk in array

mdadm /dev/mdX --remove /dev/sdX

Change disk quantity in array

mdadm --grow /dev/mdX --raid-devices=X

Switch to RW

mdadm --readwrite /dev/mdX

Show details of array

mdadm --detail /dev/md0

Show arrays status

cat /proc/mdstat