Add a spare to a poorly defined raid1

[David Liontooth <lionteeth@cogweb.net>]

Not knowing what I was doing, I created a RAID1 with a single drive and 
a spare, as below.

I'd like to add the spare to the array. How do I do this without rebooting?

Cheers,
Dave


# definitions of existing MD arrays
ARRAY /dev/md0 level=raid1 num-devices=1 
UUID=9921faab:5d93510e:0db287f1:dc103b07
    spares=1

# mdadm --detail /dev/md0
/dev/md0:
         Version : 0.90
   Creation Time : Fri Jul 18 14:57:40 2008
      Raid Level : raid1
      Array Size : 104320 (101.89 MiB 106.82 MB)
   Used Dev Size : 104320 (101.89 MiB 106.82 MB)
    Raid Devices : 1
   Total Devices : 2
Preferred Minor : 0
     Persistence : Superblock is persistent

     Update Time : Wed Feb 15 03:37:11 2012
           State : clean
  Active Devices : 1
Working Devices : 2
  Failed Devices : 0
   Spare Devices : 1

            UUID : 9921faab:5d93510e:0db287f1:dc103b07
          Events : 0.218

     Number   Major   Minor   RaidDevice State
        0       8        1        0      active sync   /dev/sda1

        1       8       17        -      spare   /dev/sdb1