Replace failed disk

This is just a note about replacing a raid member

user@vrem:~$ cat /proc/mdstat
Personalities : [raid1] [raid6] [raid5] [raid4] [linear] [multipath] [raid0] [raid10]
md127 : active raid5 sda1[4](F) sdb1[0] sdd1[2] sdc1[1]
      11720653824 blocks super 1.2 level 5, 512k chunk, algorithm 2 [4/3] [UUU_]
      bitmap: 30/30 pages [120KB], 65536KB chunk

user@vrem:~$ lsblk
NAME        MAJ:MIN RM   SIZE RO TYPE  MOUNTPOINTS
loop0         7:0    0  63,8M  1 loop  /snap/core20/2686
loop1         7:1    0  63,8M  1 loop  /snap/core20/2682
loop2         7:2    0  91,4M  1 loop  /snap/lxd/36558
loop3         7:3    0  91,4M  1 loop  /snap/lxd/36918
loop4         7:4    0  50,9M  1 loop  /snap/snapd/25577
loop5         7:5    0  48,1M  1 loop  /snap/snapd/25935
sda           8:0    0   3,6T  0 disk
└─sda1        8:1    0   3,6T  0 part
  └─md127     9:127  0  10,9T  0 raid5 /WBACKUP
sdb           8:16   0   3,6T  0 disk
└─sdb1        8:17   0   3,6T  0 part
  └─md127     9:127  0  10,9T  0 raid5 /WBACKUP
sdc           8:32   0   3,6T  0 disk
└─sdc1        8:33   0   3,6T  0 part
  └─md127     9:127  0  10,9T  0 raid5 /WBACKUP
sdd           8:48   0   3,6T  0 disk
└─sdd1        8:49   0   3,6T  0 part
  └─md127     9:127  0  10,9T  0 raid5 /WBACKUP
sde           8:64   0   3,6T  0 disk
sdf           8:80   0   3,6T  0 disk

user@vrem:~$ sudo fdisk /dev/sde

g - create GPT for 2TB+
n - create new partition
1 - number of part, 1 is default
enter - start sector  (2048 is deafault)
enter - end sector (100% is default)
w - write changes
t - change type. it is recomendation
29 - Linux RAID (for list use L)
w - write changes
q - quit

NOTE! check the number of bytes and sectors on your new partition, it should not less than that of other RAID members.

user@vrem:~$ sudo mdadm /dev/md127 --remove /dev/sda1 --verbose
mdadm: hot removed /dev/sda1 from /dev/md127
user@vrem:~$ sudo mdadm --zero-superblock /dev/sde1
user@vrem:~$ sudo mdadm /dev/md127 --add /dev/sde1
mdadm: added /dev/sde1

user@vrem:~$ cat /proc/mdstat
Personalities : [raid1] [raid6] [raid5] [raid4] [linear] [multipath] [raid0] [raid10]
md127 : active raid5 sde1[4] sdb1[0] sdd1[2] sdc1[1]
      11720653824 blocks super 1.2 level 5, 512k chunk, algorithm 2 [4/3] [UUU_]
      [>....................]  recovery =  0.0% (626756/3906884608) finish=311.6min speed=208918K/sec
      bitmap: 30/30 pages [120KB], 65536KB chunk