mdstat

gacanepa@alumno:~$ cat /proc/mdstat
Personalities : [raid1]
unused devices: <none>
gacanepa@alumno:~$ sudo mdadm -Cv /dev/md0 -l1 -n2 /dev/sdc /dev/sdd
mdadm: partition table exists on /dev/sdc but will be lost or
       meaningless after creating array
mdadm: Note: this array has metadata at the start and
    may not be suitable as a boot device.  If you plan to
    store '/boot' on this device please ensure that
    your boot-loader understands md/v1.x metadata, or use
    --metadata=0.90
mdadm: partition table exists on /dev/sdd but will be lost or
       meaningless after creating array
mdadm: size set to 7912436K
Continue creating array? y
mdadm: Defaulting to version 1.2 metadata
mdadm: array /dev/md0 started.
gacanepa@alumno:~$ cat /proc/mdstat
Personalities : [raid1]
md0 : active raid1 sdd[1] sdc[0]
      7912436 blocks super 1.2 [2/2] [UU]
      [>....................]  resync =  0.5% (44480/7912436) finish=35.3min speed=3706K/sec
unused devices: <none>