root@omv30:~# cat /proc/mdstat
Personalities : [raid1] [linear] [multipath] [raid0] [raid6] [raid5] [raid4] [raid10] 
md0 : active raid1 sdc[2] sdb[0]
      1047552 blocks super 1.2 [2/2] [UU]
      
unused devices: <none>

已经重建成功。

2、热插拔硬盘测试

在VirtualBox的存储中，勾选sdb的热插拔，然后启动。
系统在运行时，到VirtualBox的存储中移除sdb硬盘，然后查看状态：

root@omv30:~# mdadm -D /dev/md0 
/dev/md0:
        Version : 1.2
  Creation Time : Sun Sep 30 22:31:39 2018
     Raid Level : raid1
     Array Size : 1047552 (1023.00 MiB 1072.69 MB)
  Used Dev Size : 1047552 (1023.00 MiB 1072.69 MB)
   Raid Devices : 2
  Total Devices : 1
    Persistence : Superblock is persistent

    Update Time : Mon Oct  1 21:13:45 2018
          State : clean, degraded 
 Active Devices : 1
Working Devices : 1
 Failed Devices : 0
  Spare Devices : 0

           Name : omv30:raid1  (local to host omv30)
           UUID : 921a8946:b273e00e:3fa4b99d:040a4437
         Events : 56

    Number   Major   Minor   RaidDevice State
       -       0        0        0      removed
       2       8       32        1      active sync   /dev/sdc

查看系统日志，发现有硬盘离线，并且RAID1降级（有日志跟踪是软RAID的一个优势）：

root@omv30:/var/log# dmesg | tail -20
[  340.551533] md: recovery of RAID array md0
[  345.881625] md: md0: recovery done.
[  657.932091] EXT4-fs (md0): mounted filesystem with ordered data mode. Opts: (null)
[ 2571.324851] ata2: SATA link down (SStatus 0 SControl 300)
[ 2576.667851] ata2: SATA link down (SStatus 0 SControl 300)
[ 2582.044796] ata2: SATA link down (SStatus 0 SControl 300)
[ 2582.044864] ata2.00: disabled
[ 2582.045573] ata2.00: detaching (SCSI 3:0:0:0)
[ 2582.058467] sd 3:0:0:0: [sdb] Synchronizing SCSI cache
[ 2582.058528] sd 3:0:0:0: [sdb] Synchronize Cache(10) failed: Result: hostbyte=DID_BAD_TARGET driverbyte=DRIVER_OK
[ 2582.058536] sd 3:0:0:0: [sdb] Stopping disk
[ 2582.058552] sd 3:0:0:0: [sdb] Start/Stop Unit failed: Result: hostbyte=DID_BAD_TARGET driverbyte=DRIVER_OK
[ 2586.709149] md/raid1:md0: Disk failure on sdb, disabling device.
               md/raid1:md0: Operation continuing on 1 devices.

加入新硬盘。新加的硬盘不能比现有的小，可以比现在的大。

root@omv30:~# mdadm /dev/md0 --add /dev/sdc

开始重建：

root@omv30:~# mdadm -D /dev/md0 
/dev/md0:
        Version : 1.2
  Creation Time : Sun Sep 30 22:31:39 2018
     Raid Level : raid1
     Array Size : 1047552 (1023.00 MiB 1072.69 MB)
  Used Dev Size : 1047552 (1023.00 MiB 1072.69 MB)
   Raid Devices : 2
  Total Devices : 2
    Persistence : Superblock is persistent

    Update Time : Mon Oct  1 21:38:36 2018
          State : clean, degraded, recovering 
 Active Devices : 1
Working Devices : 2
 Failed Devices : 0
  Spare Devices : 1

 Rebuild Status : 56% complete

           Name : omv30:raid1  (local to host omv30)
           UUID : 921a8946:b273e00e:3fa4b99d:040a4437
         Events : 69

    Number   Major   Minor   RaidDevice State
       3       8       32        0      spare rebuilding   /dev/sdc
       2       8       16        1      active sync   /dev/sdb

root@omv30:~# cat /proc/mdstat 
Personalities : [raid1] [linear] [multipath] [raid0] [raid6] [raid5] [raid4] [raid10] 
md0 : active raid1 sdc[3] sdb[2]
      1047552 blocks super 1.2 [2/1] [_U]
      [===================>.]  recovery = 95.0% (996288/1047552) finish=0.0min speed=249072K/sec
      
unused devices: <none>

重建完成：