How to create, add and remove block devices to the Raid device on Ubuntu 21.04

To Create, add and remove block devices to the Raid device on Ubuntu 21.04

Introduction:

The RAID device is a virtual device created from two or more real block devices that allows multiple devices to be combined into one and hold a single file system. A Linux Software RAID device is implemented using the MD device driver (Multiple Devices).

Step 1: Check the installed OS version by using the following command

root@linuxhelp:~# lsb_release -a
No LSB modules are available.
Distributor ID:	Ubuntu
Description:	Ubuntu 21.04
Release:	21.04
Codename:	hirsute

Step 2: Install mdadm package by using the following command

root@linuxhelp:~# apt install mdadm
Reading package lists... Done
Building dependency tree... Done
Reading state information... Done
The following packages were automatically installed and are no longer required:
  libllvm11 net-tools
Use 'apt autoremove' to remove them.
The following additional packages will be installed:
  finalrd
Suggested packages:
  default-mta | mail-transport-agent dracut-core
The following NEW packages will be installed:
  finalrd mdadm
0 upgraded, 2 newly installed, 0 to remove and 0 not upgraded.
Need to get 430 kB of archives.
After this operation, 1,299 kB of additional disk space will be used.
Do you want to continue? [Y/n] y
Get:1 http://in.archive.ubuntu.com/ubuntu hirsute/main amd64 finalrd all 7 [6,860 B]
Get:2 http://in.archive.ubuntu.com/ubuntu hirsute/main amd64 mdadm amd64 4.1-10ubuntu3 [423 kB]
Fetched 430 kB in 1s (833 kB/s)
Preconfiguring packages ...
Selecting previously unselected package finalrd.
(Reading database ... 209649 files and directories currently installed.)
Preparing to unpack .../apt/archives/finalrd_7_all.deb ...
Unpacking finalrd (7) ...
Selecting previously unselected package mdadm.
Preparing to unpack .../mdadm_4.1-10ubuntu3_amd64.deb ...
Unpacking mdadm (4.1-10ubuntu3) ...
Setting up finalrd (7) ...
Created symlink /etc/systemd/system/sysinit.target.wants/finalrd.service → /lib/systemd/system/finalrd.service.
Setting up mdadm (4.1-10ubuntu3) ...
Generating mdadm.conf... done.
update-initramfs: deferring update (trigger activated)
Sourcing file `/etc/default/grub'
Created symlink /etc/systemd/system/mdmonitor.service.wants/mdcheck_continue.timer → /lib/systemd/system/mdcheck_continu
e.timer.
Created symlink /etc/systemd/system/mdmonitor.service.wants/mdcheck_start.timer → /lib/systemd/system/mdcheck_start.time
r.
Created symlink /etc/systemd/system/mdmonitor.service.wants/mdmonitor-oneshot.timer → /lib/systemd/system/mdmonitor-ones
hot.timer.
Processing triggers for man-db (2.9.4-2) ...
Processing triggers for initramfs-tools (0.139ubuntu3) ...
update-initramfs: Generating /boot/initrd.img-5.11.0-40-generic

Step 3: Open fdisk to create partions on /dev/sdb disk

root@linuxhelp:~# fdisk /dev/sdb

Welcome to fdisk (util-linux 2.36.1).
Changes will remain in memory only, until you decide to write them.
Be careful before using the write command.

Device does not contain a recognized partition table.
Created a new DOS disklabel with disk identifier 0xec47ae17.



Creating New Partition

Command (m for help): n
Partition type
   p   primary (0 primary, 0 extended, 4 free)
   e   extended (container for logical partitions)
Select (default p): 

Using default response p.

Using default partition number and using entire disk space partition by pressing enter for all
Partition number (1-4, default 1): 
First sector (2048-41943039, default 2048): 
Last sector, +/-sectors or +/-size{K,M,G,T,P} (2048-41943039, default 41943039): 

Created a new partition 1 of type 'Linux' and of size 20 GiB.


Changing the partition type to Linux raid autodetect 
Command (m for help): t

Selected partition 1
Hex code or alias (type L to list all): fd
Changed type of partition 'Linux' to 'Linux raid autodetect'.



Saving the all changes made to the disks
Command (m for help): w

The partition table has been altered.
Calling ioctl() to re-read partition table.
Syncing disks.

Step 4: Open fdisk to create partions on /dev/sdc disk

root@linuxhelp:~# fdisk /dev/sdc

Welcome to fdisk (util-linux 2.36.1).
Changes will remain in memory only, until you decide to write them.
Be careful before using the write command.

Device does not contain a recognized partition table.
Created a new DOS disklabel with disk identifier 0xa183b98d.

Creating New Partition
Command (m for help): n
Partition type
   p   primary (0 primary, 0 extended, 4 free)
   e   extended (container for logical partitions)
Select (default p): 

Using default response p.


Using default partition number and using entire disk space partition by pressing enter for all
Partition number (1-4, default 1): 
First sector (2048-41943039, default 2048): 
Last sector, +/-sectors or +/-size{K,M,G,T,P} (2048-41943039, default 41943039): 

Created a new partition 1 of type 'Linux' and of size 20 GiB.




Change the partition type to Linux LVM 
Command (m for help): t

Selected partition 1
Hex code or alias (type L to list all): fd
Changed type of partition 'Linux' to 'Linux raid autodetect'.


Save the all changes made to the disks
Command (m for help): w
The partition table has been altered.
Calling ioctl() to re-read partition table.
Syncing disks.

root@linuxhelp:~# mdadm -C /dev/md0 -l 1 -n 2 /dev/sd[b-c]1
mdadm: Note: this array has metadata at the start and
    may not be suitable as a boot device.  If you plan to
    store '/boot' on this device please ensure that
    your boot-loader understands md/v1.x metadata, or use
    --metadata=0.90
Continue creating array? 
Continue creating array? (y/n) y
mdadm: Defaulting to version 1.2 metadata
mdadm: array /dev/md0 started.

root@linuxhelp:~# mdadm --detail /dev/md0
/dev/md0:
           Version : 1.2
     Creation Time : Mon Nov 29 19:19:08 2021
        Raid Level : raid1
        Array Size : 20953088 (19.98 GiB 21.46 GB)
     Used Dev Size : 20953088 (19.98 GiB 21.46 GB)
      Raid Devices : 2
     Total Devices : 2
       Persistence : Superblock is persistent

       Update Time : Mon Nov 29 19:19:27 2021
             State : clean, resyncing 
    Active Devices : 2
   Working Devices : 2
    Failed Devices : 0
     Spare Devices : 0

Consistency Policy : resync

     Resync Status : 20% complete

              Name : linuxhelp:0  (local to host linuxhelp)
              UUID : f925a91a:86f15757:d4721be4:5f6ccd45
            Events : 3

    Number   Major   Minor   RaidDevice State
       0       8       17        0      active sync   /dev/sdb1
       1       8       33        1      active sync   /dev/sdc1

root@linuxhelp:~# mkfs.ext4 /dev/md0
mke2fs 1.45.7 (28-Jan-2021)
Creating filesystem with 5238272 4k blocks and 1310720 inodes
Filesystem UUID: 34ab81ad-6dd4-40fc-aba5-9c93acc37cb9
Superblock backups stored on blocks: 
	32768, 98304, 163840, 229376, 294912, 819200, 884736, 1605632, 2654208, 
	4096000

Allocating group tables: done                            
Writing inode tables: done                            
Creating journal (32768 blocks): done
Writing superblocks and filesystem accounting information: done   

root@linuxhelp:~# mkdir /raid1

root@linuxhelp:~# mount /dev/md0 /raid1

root@linuxhelp:~# vi /raid1/test

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root@linuxhelp:~# vi /etc/fstab
/dev/md0                /raid1              ext4    defaults        0 0

root@linuxhelp:~# mount -a

root@linuxhelp:~# mdadm -f /dev/md0 /dev/sdc1
mdadm: set /dev/sdc1 faulty in /dev/md0

root@linuxhelp:~# mdadm --remove /dev/md0 /dev/sdc1
mdadm: hot removed /dev/sdc1 from /dev/md0

root@linuxhelp:~# mdadm --detail /dev/md0
/dev/md0:
           Version : 1.2
     Creation Time : Mon Nov 29 19:19:08 2021
        Raid Level : raid1
        Array Size : 20953088 (19.98 GiB 21.46 GB)
     Used Dev Size : 20953088 (19.98 GiB 21.46 GB)
      Raid Devices : 2
     Total Devices : 1
       Persistence : Superblock is persistent

       Update Time : Mon Nov 29 19:23:18 2021
             State : clean, degraded 
    Active Devices : 1
   Working Devices : 1
    Failed Devices : 0
     Spare Devices : 0

Consistency Policy : resync

              Name : linuxhelp:0  (local to host linuxhelp)
              UUID : f925a91a:86f15757:d4721be4:5f6ccd45
            Events : 28

    Number   Major   Minor   RaidDevice State
       0       8       17        0      active sync   /dev/sdb1
       -       0        0        1      removed

root@linuxhelp:~# cat /raid1/test

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