Something

root@brocco:~# mdadm /dev/md0 --fail /dev/sde1
mdadm: set /dev/sde1 faulty in /dev/md0
root@brocco:~# mdadm /dev/md0 --remove /dev/sde1
mdadm: hot removed /dev/sde1
root@brocco:~# mdadm /dev/md0 --re-add /dev/sde1
mdadm: re-added /dev/sde1
root@brocco:~# mdadm /dev/md0 --brief
/dev/md0: 232.84GiB raid1 2 devices, 1 spare. Use mdadm --detail for more detail.
root@brocco:~# mdadm /dev/md0 --detail
root@brocco:~#