How to replace Faulty Linux RAID disk

When the disk is partitioned, you can add it back to the array as follows:

[root@rhel1 ~]# mdadm /dev/md1 -a /dev/sdd1
mdadm: added /dev/sdd1

Verify that it has been added properly, you can see that its in rebuilding phase:

[root@rhel1 ~]# mdadm -D /dev/md1
/dev/md1:
Version : 1.2
Creation Time : Wed Dec 7 19:05:53 2016
Raid Level : raid5
Array Size : 2087936 (2039.34 MiB 2138.05 MB)
Used Dev Size : 1043968 (1019.67 MiB 1069.02 MB)
Raid Devices : 3
Total Devices : 3
Persistence : Superblock is persistent

Update Time : Wed Dec 7 19:09:35 2016
State : clean, degraded, recovering
Active Devices : 2
Working Devices : 3
Failed Devices : 0
Spare Devices : 1

Layout : left-symmetric
Chunk Size : 512K

Rebuild Status : 10% complete

Name : rhel1.lab.com:1 (local to host rhel1.lab.com)
UUID : fcef1f48:223e87c7:53e9eecc:d5f55e79
Events : 50

Number Major Minor RaidDevice State
0 8 33 0 active sync /dev/sdc1
4 8 49 1 spare rebuilding /dev/sdd1
3 8 65 2 active sync /dev/sde1

After some time all will become in active:sync state as below:

[root@rhel1 ~]# mdadm -D /dev/md1
/dev/md1:
Version : 1.2
Creation Time : Wed Dec 7 19:05:53 2016
Raid Level : raid5
Array Size : 2087936 (2039.34 MiB 2138.05 MB)
Used Dev Size : 1043968 (1019.67 MiB 1069.02 MB)
Raid Devices : 3
Total Devices : 3
Persistence : Superblock is persistent

Update Time : Wed Dec 7 19:09:39 2016
State : clean
Active Devices : 3
Working Devices : 3
Failed Devices : 0
Spare Devices : 0

Layout : left-symmetric
Chunk Size : 512K

Name : rhel1.lab.com:1 (local to host rhel1.lab.com)
UUID : fcef1f48:223e87c7:53e9eecc:d5f55e79
Events : 68

Number Major Minor RaidDevice State
0 8 33 0 active sync /dev/sdc1
4 8 49 1 active sync /dev/sdd1
3 8 65 2 active sync /dev/sde1
[root@rhel1 ~]#