Step-by-step guide

1. Mark the drive as failed
   

   1	$ sudo mdadm --manage /dev/md0 --fail /dev/sdb1

2. Remove the drive from the array
   

   1	$ sudo mdadm --manage /dev/md0 --remove /dev/sdb1

3. View the mdadm status
   

   1	$ cat /proc/mdstat

4. If you prefer to shut down the system for a cold swap, do it now. Before the hot swap, put the drive into standby with the following command
   

   1	$ sudo hdparm -Y /dev/sdb

   
   Make sure you know which drive you are going to remove before issuing this command. Operations to the disk will wake up the drive again.
5. Remove the SATA signal cable first and then the SATA power cable.
6. Mount the new drive and connect SATA power. I let the drive spin up for 5-10 seconds before connecting the SATA signal cable. If you did a cold swap, power on the system at this point.
7. Identify the new drive and what device name it has. In my case, the new drive was conveniently named /dev/sdb, the same as the old one.
8. Copy the partitioning setup from the other drive in the array to the new disk. (This is for a RAID1 setup)
   Make sure the order is correct, otherwise we will erase the operational drive!
   

   1	$ sfdisk -d /dev/sdc | sfdisk /dev/sdb

9. Add the new drive to the RAID array
   

   1	$ sudo mdadm --manage /dev/md0 --add /dev/sdb1

10. The RAID array will now be rebuilt and the progress is indicated by the
    

    1	$ cat /proc/mdstat

    
    output. To have a more dynamic update of the progress use the following:
    

    1	$ watch cat /proc/mdstat