UbuntuファイルサーバーのRAIDにエラーが・・・

ある日メールがきました

タイトル
Fail event on /dev/md0:XXXX

本文

This is an automatically generated mail message from mdadm
running on XXXX

A Fail event had been detected on md device /dev/md0.

It could be related to component device /dev/sdb4.

Faithfully yours, etc.

P.S. The /proc/mdstat file currently contains the following:

Personalities : [linear] [multipath] [raid0] [raid1] [raid6] [raid5] [raid4] [raid10] 
md0 : active raid1 sdb4[2](F) sda4[0]
      1926248384 blocks [2/1] [U_]
      
unused devices: <none>

どういうことだってばよ・・・

状況を確認してみました 

$ sudo mdadm --detail /dev/md0

/dev/md0:
        Version : 00.90
  Creation Time : Sat Aug 28 15:36:43 2010
     Raid Level : raid1
     Array Size : 1926248384 (1837.01 GiB 1972.48 GB)
  Used Dev Size : 1926248384 (1837.01 GiB 1972.48 GB)
   Raid Devices : 2
  Total Devices : 2
Preferred Minor : 0
    Persistence : Superblock is persistent

    Update Time : Sun Jan  8 20:51:23 2012
          State : clean, degraded
 Active Devices : 1
Working Devices : 1
 Failed Devices : 1
  Spare Devices : 0

           UUID : ce836218:f86924b6:5c2ef4e7:4e679ae8 (local to host XXXX)
         Events : 0.13614

    Number   Major   Minor   RaidDevice State
       0       8        4        0      active sync   /dev/sda4
       1       0        0        1      removed

       2       8       20        -      faulty spare   /dev/sdb4

どうやらsbd4の方がダメなようです。
次の休みに調べてみるかなぁ。
どうすればいいんだろう。raidを解除してフォーマットしてみる・・・？

(20120117追記)
マシン再起動したら直ったようで・・・

$ sudo mdadm --detail /dev/md0
/dev/md0:
        Version : 00.90
  Creation Time : Sat Aug 28 15:36:43 2010
     Raid Level : raid1
     Array Size : 1926248384 (1837.01 GiB 1972.48 GB)
  Used Dev Size : 1926248384 (1837.01 GiB 1972.48 GB)
   Raid Devices : 2
  Total Devices : 2
Preferred Minor : 0
    Persistence : Superblock is persistent

    Update Time : Tue Jan 17 17:14:15 2012
          State : clean, degraded, recovering
 Active Devices : 1
Working Devices : 2
 Failed Devices : 0
  Spare Devices : 1

 Rebuild Status : 7% complete

           UUID : ce836218:f86924b6:5c2ef4e7:4e679ae8 (local to host XXXX)
         Events : 0.36952

    Number   Major   Minor   RaidDevice State
       0       8        4        0      active sync   /dev/sda4
       2       8       20        1      spare rebuilding   /dev/sdb4