mdadm failed

gacanepa@debian:~$ sudo mdadm -D /dev/md0
/dev/md0:
        Version : 1.2
  Creation Time : Sat Jan 26 15:01:57 2013
     Raid Level : raid1
     Array Size : 7912436 (7.55 GiB 8.10 GB)
  Used Dev Size : 7912436 (7.55 GiB 8.10 GB)
   Raid Devices : 2
  Total Devices : 2
    Persistence : Superblock is persistent

    Update Time : Sat Jan 26 15:09:48 2013
          State : clean, degraded
 Active Devices : 1
Working Devices : 1
 Failed Devices : 1
  Spare Devices : 0

           Name : debian:0  (local to host debian)
           UUID : 461a5937:b35162a8:85d6aa25:00ef2941
         Events : 14

    Number   Major   Minor   RaidDevice State
       0       0        0        0      removed
       1       8       48        1      active sync   /dev/sdd

       0       8       32        -      faulty spare