trouble adding spare

Hi,

I have a RAID5 array using 6 disks and 2 spares. I took one spare away for a few months for another purpose (OS X) and am having trouble adding it back in as a spare.

I can add it manually :

sudo /sbin/mdadm /dev/md2 -a /dev/sdi

but it doesn't want to add itself in after rebooting (the other spare is added ok).

I'm sure this is simple for someone...

Max.

/dev/md2:
       Version : 00.90
 Creation Time : Sat Aug  6 05:18:41 2005
    Raid Level : raid5
    Array Size : 976804480 (931.55 GiB 1000.25 GB)
 Used Dev Size : 195360896 (186.31 GiB 200.05 GB)
  Raid Devices : 6
 Total Devices : 8
Preferred Minor : 2
   Persistence : Superblock is persistent

   Update Time : Wed Jan 14 11:27:11 2009
         State : clean
Active Devices : 6
Working Devices : 8
Failed Devices : 0
 Spare Devices : 2

        Layout : left-symmetric
    Chunk Size : 64K

          UUID : 15bfec75:595ac793:0914f8ee:862effd8
        Events : 0.9341278

   Number   Major   Minor   RaidDevice State
      0       8       80        0      active sync   /dev/sdf
      1       8       96        1      active sync   /dev/sdg
      2       8       16        2      active sync   /dev/sdb
      3       8       48        3      active sync   /dev/sdd
      4       8       32        4      active sync   /dev/sdc
      5       8       64        5      active sync   /dev/sde

      6       8      128        -      spare   /dev/sdi
      7       8      112        -      spare   /dev/sdh

..../etc/mdadm/mdadm.conf
DEVICE /dev/sd[bcdefghi]

# auto-create devices with Debian standard permissions
CREATE owner=root group=disk mode=0660 auto=yes

# automatically tag new arrays as belonging to the local system
HOMEHOST <system>

# instruct the monitoring daemon where to send mail alerts
MAILADDR davidmaxwaterman@fastmail.co.uk

# definitions of existing MD arrays
ARRAY /dev/md2 level=raid5 num-devices=6 UUID=15bfec75:595ac793:0914f8ee:862effd8 spares=2