Replacing HDD and rebuild linux raid1 with mdadmn


1) fdisk -l 
Record the partition size


2) watch cat /proc/mdstat 
Then open other terminal console


3) 
server1:~# mdadm --manage /dev/md0 --fail /dev/sdb1
server1:~# mdadm --manage /dev/md0 --remove /dev/sdb1


4) 
server1:~# mdadm --manage /dev/md1 --fail /dev/sdb2
server1:~# mdadm --manage /dev/md1 --remove /dev/sdb2

Repeat  3~4 , if you have /dev/mdX with member /dev/sdbX


5) hdparm -I /dev/sdb |grep Serial

To know the problem disk serial number 


6) Shutdown and Replace problem HDD (check serial number) , Start back server


7) fdisk /dev/sdb 
Create the same partition sizes as  same as old bad hdd record


8) 
server1:~# mdadm --manage /dev/md0 --add /dev/sdb1
server1:~# mdadm --manage /dev/md1 --add /dev/sdb2


9) server1:~# watch cat /proc/mdstat
Every 2.0s: cat /proc/mdstat
Personalities : [raid1]
md0 : active raid1 sda1[0] sdb1[1]
      24418688 blocks [2/1] [U_]
      [=>...................]  recovery =  9.9% (2423168/24418688) finish=2.8min speed=127535K/sec

md1 : active raid1 sda2[0] sdb2[1]
      24418688 blocks [2/1] [U_]
      [=>...................]  recovery =  6.4% (1572096/24418688) finish=1.9min speed=196512K/sec