How to replace Faulty Linux RAID disk

Check the status of md1

[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 19:07:26 2016
State : clean, degraded
Active Devices : 2
Working Devices : 2
Failed Devices : 1
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 : 19

Number Major Minor RaidDevice State
0 8 33 0 active sync /dev/sdc1
1 0 0 1 removed
3 8 65 2 active sync /dev/sde1

1 8 49 - faulty spare /dev/sdd1

you can see that /dev/sdd1 is marked as faulty now remove the same from configuration using below command:

[root@rhel1 ~]# mdadm /dev/md1 -r /dev/sdd1
mdadm: hot removed /dev/sdd1 from /dev/md1

When you have replace Faulty Linux RAID disk, you need to make it active in the array. First, you need to partition the disk like you did originally when setting up the RAID array.