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1. Create RAID-1 level array with 2 active devices and 1 spare:
   
   # mdadm -C /dev/md0 -l 1 -n 2 /dev/hda{8,9} -x 1 /dev/hda10

   Note: RAID-1 provides for redundancy and needs a minimum of 2 partitions and any number of spares.

2. Show details:
   
   # mdadm --detail /dev/md0
3. Mark Faulty:
   
   # mdadm --manage /dev/md0 -f /dev/hda8

   Note: When partition is marked faulty, the spare quickly replaces it in RAID 1 array.

4. Remove:
   
   # mdadm --manage /dev/md0 -r /dev/hda8

   Note: Only faulty partitions can be removed.

5. Add:
   
   # mdadm --manage /dev/md0 -a /dev/hda8

   Note: Only removed partitions can be added.

6. Stop RAID:
   
   # mdadm --stop /dev/md0
7. Run RAID:
   
   # mdadm --assemble /dev/md0 /dev/hda{8,9,10}

   Note: Before assembling, check on the UUID of the devices. They should all be the same and show only one array:
   

   mdadm --examine --scan /dev/hda{8,9,10}

8. Remove the md signature from disk
   
   # mdadm --zero-superblock /dev/hda{8,9,10}
9. Scan md superblock
   
   # mdadm --examine --scan
10. Scan currently active arrays
    
    mdadm --detail --scan
11. Monitor RAID:
    
    # nohup mdadm --monitor --mail=root --delay=300 /dev/md0 &

Related Links:

• Software-RAID.HOWTO