Failed Raid 1 device & wants to readd again(assume the harddisk is status normal)

Raid Status but make sure both harddisk are normal and without bad sector.

[root@server ~]# cat /proc/mdstat
Personalities : [raid1]
md2 : active raid1 sda2[0] sdb2[2](F)
      156183808 blocks [2/1] [U_]

md1 : active raid1 sda1[0] sdb1[1]
      104320 blocks [2/2] [UU]

unused devices:

************************************************
if you want to fail the device by command, use this
[root@server ~]#  mdadm /dev/md2 --fail /dev/sdb2
************************************************

* User command to remove the failed device.

[root@server ~]#  mdadm /dev/md2 --remove /dev/sdb2

[root@server ~]# cat /proc/mdstat

Personalities : [raid1]

md2 : active raid1 sda2[0]

      156183808 blocks [2/1] [U_]

md1 : active raid1 sda1[0] sdb1[1]

      104320 blocks [2/2] [UU]

unused devices:

[root@server ~]# mdadm /dev/md2 --add /dev/sdb2

mdadm: hot added /dev/sdb2

[root@server ~]# cat /proc/mdstat

Personalities : [raid1]

md2 : active raid1 sdb2[2] sda2[0]

      156183808 blocks [2/1] [U_]

      [>....................]  recovery =  0.1% (185024/156183808) finish=28.0min speed=92512K/sec

md1 : active raid1 sda1[0] sdb1[1]

      104320 blocks [2/2] [UU]

unused devices: