其实很简单，在万一真出问题前演练一下没准扣我少点工资（

参考网站：https://www.howtoforge.com/how-to-set-up-software-raid1-on-a-running-lvm-system-incl-grub-configuration-centos-5.3-p4

假设有sda和sdb两个盘并组了raid1

这里的情况是sdb突然爆炸了，无法使用。

可以使用mdadm模拟这种情况：

 mdadm --manage /dev/md0 --fail /dev/sdb1
 mdadm --manage /dev/md1 --fail /dev/sdb2

或者模拟暴力移除：

mdadm --manage /dev/md0 --remove /dev/sdb1
mdadm --manage /dev/md1 --remove /dev/sdb2

reboot重启一下

运行

cat /proc/mdstat

查看当前磁盘raid情况

[root@server1 ~]# cat /proc/mdstat
Personalities : [raid1]
md0 : active raid1 sda1[0]
      104320 blocks [2/1] [U_]

md1 : active raid1 sda2[0]
      10377920 blocks [2/1] [U_]

unused devices: <none>
[root@server1 ~]#

也可以使用fdisk

fdisk -l
[root@server1 ~]# fdisk -l

Disk /dev/sda: 10.7 GB, 10737418240 bytes
255 heads, 63 sectors/track, 1305 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes

   Device Boot      Start         End      Blocks   Id  System
/dev/sda1   *           1          13      104391   fd  Linux raid autodetect
/dev/sda2              14        1305    10377990   fd  Linux raid autodetect

Disk /dev/sdb: 10.7 GB, 10737418240 bytes
255 heads, 63 sectors/track, 1305 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes

Disk /dev/sdb doesn't contain a valid partition table

Disk /dev/md1: 10.6 GB, 10626990080 bytes
2 heads, 4 sectors/track, 2594480 cylinders
Units = cylinders of 8 * 512 = 4096 bytes

Disk /dev/md1 doesn't contain a valid partition table

Disk /dev/md0: 106 MB, 106823680 bytes
2 heads, 4 sectors/track, 26080 cylinders
Units = cylinders of 8 * 512 = 4096 bytes

Disk /dev/md0 doesn't contain a valid partition table
[root@server1 ~]#

假设现在新的好硬盘sdb已经换上了

先同步一下分区表

sfdisk -d /dev/sda | sfdisk /dev/sdb
[root@server1 ~]# sfdisk -d /dev/sda | sfdisk /dev/sdb
Checking that no-one is using this disk right now ...
OK

Disk /dev/sdb: 1305 cylinders, 255 heads, 63 sectors/track

sfdisk: ERROR: sector 0 does not have an msdos signature
 /dev/sdb: unrecognized partition table type
Old situation:
No partitions found
New situation:
Units = sectors of 512 bytes, counting from 0

   Device Boot    Start       End   #sectors  Id  System
/dev/sdb1   *        63    208844     208782  fd  Linux raid autodetect
/dev/sdb2        208845  20964824   20755980  fd  Linux raid autodetect
/dev/sdb3             0         -          0   0  Empty
/dev/sdb4             0         -          0   0  Empty
Successfully wrote the new partition table

Re-reading the partition table ...

If you created or changed a DOS partition, /dev/foo7, say, then use dd(1)
to zero the first 512 bytes:  dd if=/dev/zero of=/dev/foo7 bs=512 count=1
(See fdisk(8).)
[root@server1 ~]#

同时，可能新硬盘其实是个二手硬盘以前做过raid，这时我们需要把sdb里的raid记录清空一遍。

mdadm --zero-superblock /dev/sdb1
mdadm --zero-superblock /dev/sdb2

然后我们就可以把硬盘和以前的硬盘组起来了

mdadm -a /dev/md0 /dev/sdb1
mdadm -a /dev/md1 /dev/sdb2

然后就可以查看硬盘数据恢复情况了

cat /proc/mdstat
[root@server1 ~]# cat /proc/mdstat
Personalities : [raid1]
md0 : active raid1 sdb1[1] sda1[0]
      104320 blocks [2/2] [UU]

md1 : active raid1 sdb2[2] sda2[0]
      10377920 blocks [2/1] [U_]
      [======>..............]  recovery = 32.3% (3360768/10377920) finish=1.5min speed=74238K/sec

unused devices: <none>
[root@server1 ~]#

还有，不要忘记给两个硬盘都重新安装引导！

grub：

grub

root (hd0,0)
setup (hd0)
root (hd1,0)
setup (hd1)
quit

grub2:

grub2-install /dev/sda
grub2-install /dev/sdb

syslinux:

略