# Check the array
cat /proc/mdstat
mdadm --detail /dev/md0
 
# Mark it as failed
mdadm --fail /dev/md0 /dev/sdc1
 
# Remove the disk
mdadm --remove /dev/md0 /dev/sdc1
 
# Remove the array metadata from the 
#  drive to prevent reassembly on reboot
mdadm --zero-superblock /dev/sdc1