root@omv30:~# fdisk -l
Disk /dev/sda: 8 GiB, 8589934592 bytes, 16777216 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0x8c9b0fb9

Device     Boot    Start      End  Sectors Size Id Type
/dev/sda1  *        2048 12582911 12580864   6G 83 Linux
/dev/sda2       12584958 16775167  4190210   2G  5 Extended
/dev/sda5       12584960 16775167  4190208   2G 82 Linux swap / Solaris


Disk /dev/sdb: 1 GiB, 1073741824 bytes, 2097152 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes

raid1变成了inactive，但raid信息本身是保存在磁盘中，不会丢失。

4、结论

• mdadm不是根据盘符/dev/sdx来记录RAID信息的，盘符无论怎么变换，RAID信息不错乱。
• mdadm是使用Device UUID来区分硬盘的。与RAID硬盘盒不一样，硬盘盒是记录硬盘槽位号的。
• 所以mdadm每个硬盘可以使用任意硬盘盒，不用记录位置。

三、RAID降级恢复测试

场景：正常运行的RAID1，突然一块盘失效，进行重建恢复。
方法：可以用模拟fail的方式，也可以用VirtualBox热插拔硬盘的功能。

1、模拟fail的方式

初始信息如下：

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 20:29:44 2018
          State : clean 
 Active Devices : 2
Working Devices : 2
 Failed Devices : 0
  Spare Devices : 0

           Name : omv30:raid1  (local to host omv30)
           UUID : 921a8946:b273e00e:3fa4b99d:040a4437
         Events : 31

    Number   Major   Minor   RaidDevice State
       0       8       16        0      active sync   /dev/sdb
       1       8       48        1      active sync   /dev/sdd

(1)手工fail掉sdd：

root@omv30:~# mdadm /dev/md0 --fail /dev/sdd
mdadm: set /dev/sdd faulty in /dev/md0

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 20:29:59 2018
          State : clean, degraded 
 Active Devices : 1
Working Devices : 1
 Failed Devices : 1
  Spare Devices : 0

           Name : omv30:raid1  (local to host omv30)
           UUID : 921a8946:b273e00e:3fa4b99d:040a4437
         Events : 33

    Number   Major   Minor   RaidDevice State
       0       8       16        0      active sync   /dev/sdb
       -       0        0        1      removed

       1       8       48        -      faulty   /dev/sdd

如果未移除，要先移除损坏的硬盘：

root@omv30:~# mdadm /dev/md0 -r /dev/sdd
mdadm: hot remove failed for /dev/sdd: No such device or address

(2)增加新盘：

root@omv30:~# mdadm /dev/md0 --add /dev/sdc   （新加的盘是2G的，经实测不影响RAID1重建）
mdadm: added /dev/sdc
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 20:36:22 2018
          State : clean, degraded, recovering 
 Active Devices : 1
Working Devices : 2
 Failed Devices : 0
  Spare Devices : 1

 Rebuild Status : 76% complete

           Name : omv30:raid1  (local to host omv30)
           UUID : 921a8946:b273e00e:3fa4b99d:040a4437
         Events : 48

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

可以看到正在重建。
过一会儿再执行：