Linux - rebuilding a RAID array after a disk fails

Assuming that new SCSI disk is /dev/sdb, type the following command:
# raidhotadd /dev/mdX /dev/sdb

Replace /dev/mdX with actual raid device name (e.g. /dev/md0). While array is under construction, you can see progress and other information by typing following command:
# cat /proc/mdstat