/dev/md2:
        Version : 0.90
     Raid Level : raid1
     Array Size : 683792000 (652.11 GiB 700.20 GB)
  Used Dev Size : 683792000 (652.11 GiB 700.20 GB)
   Raid Devices : 2
  Total Devices : 2
Preferred Minor : 2
    Persistence : Superblock is persistent

          State : clean, degraded
 Active Devices : 1
Working Devices : 2
 Failed Devices : 0
  Spare Devices : 1

           UUID : e8ba8727:1b7ba76c:2f2051f8:e6dff55c
         Events : 0.94996850

    Number   Major   Minor   RaidDevice State
       0       8       34        0      active sync   /dev/sdc2
       2       8       50        1      spare rebuilding   /dev/sdd2

cat /sys/block/md2/md/sync_action
idle