This is the ‘old’ way of creating a RAID array. ZFS is a better way these days.
source: https://www.makeuseof.com/tag/configure-raid-hdd-array-linux/
Find the drives to be put into a RAID array
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| $ lsblk
NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINTS
sda 8:0 0 32G 0 disk
├─sda1 8:1 0 1M 0 part
├─sda2 8:2 0 2G 0 part /boot
└─sda3 8:3 0 30G 0 part
└─ubuntu--vg-ubuntu--lv 253:0 0 30G 0 lvm /
sdb 8:16 0 32G 0 disk
sdc 8:32 0 32G 0 disk
sdd 8:48 0 32G 0 disk
sde 8:64 0 32G 0 disk
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In this case, we want to use sdb, sdc, sdd, sde.
Creating RAID partitions
For each of the drives, we need to create RAID partitions.
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| $ sudo fdisk /dev/sdb
Welcome to fdisk (util-linux 2.37.2).
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 0x8afa48f9.
Command (m for help): n
Partition type
p primary (0 primary, 0 extended, 4 free)
e extended (container for logical partitions)
Select (default p): p
Partition number (1-4, default 1): 1
First sector (2048-67108863, default 2048):
Last sector, +/-sectors or +/-size{K,M,G,T,P} (2048-67108863, default 67108863):
Created a new partition 1 of type 'Linux' and of size 32 GiB.
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'.
Command (m for help): w
The partition table has been altered.
Calling ioctl() to re-read partition table.
Syncing disks.
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Notify the OS about the new partitions
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| $ sudo partprobe /dev/sdb /dev/sdc /dev/sdd /dev/sde
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You won’t see any output.
Create the array
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| $ sudo mdadm -C /dev/md0 --level=raid5 --raid-devices=4 /dev/sdb1 /dev/sdc1 /dev/sdd1 /dev/sde1
mdadm: Defaulting to version 1.2 metadata
mdadm: array /dev/md0 started.
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Monitor the new RAID array
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| $ sudo mdadm --detail /dev/md0
/dev/md0:
Version : 1.2
Creation Time : Tue Dec 6 16:48:01 2022
Raid Level : raid5
Array Size : 100608000 (95.95 GiB 103.02 GB)
Used Dev Size : 33536000 (31.98 GiB 34.34 GB)
Raid Devices : 4
Total Devices : 4
Persistence : Superblock is persistent
Update Time : Tue Dec 6 16:48:54 2022
State : clean, degraded, recovering
Active Devices : 3
Working Devices : 4
Failed Devices : 0
Spare Devices : 1
Layout : left-symmetric
Chunk Size : 512K
Consistency Policy : resync
Rebuild Status : 34% complete
Name : resize:0 (local to host resize)
UUID : fff2299a:3f00f698:70b90131:4b077662
Events : 6
Number Major Minor RaidDevice State
0 8 17 0 active sync /dev/sdb1
1 8 33 1 active sync /dev/sdc1
2 8 49 2 active sync /dev/sdd1
4 8 65 3 spare rebuilding /dev/sde1
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Once the array is done rebuilding, you will see this.
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| $ sudo mdadm --detail /dev/md0
/dev/md0:
Version : 1.2
Creation Time : Tue Dec 6 16:48:01 2022
Raid Level : raid5
Array Size : 100608000 (95.95 GiB 103.02 GB)
Used Dev Size : 33536000 (31.98 GiB 34.34 GB)
Raid Devices : 4
Total Devices : 4
Persistence : Superblock is persistent
Update Time : Tue Dec 6 16:50:49 2022
State : clean
Active Devices : 4
Working Devices : 4
Failed Devices : 0
Spare Devices : 0
Layout : left-symmetric
Chunk Size : 512K
Consistency Policy : resync
Name : resize:0 (local to host resize)
UUID : fff2299a:3f00f698:70b90131:4b077662
Events : 18
Number Major Minor RaidDevice State
0 8 17 0 active sync /dev/sdb1
1 8 33 1 active sync /dev/sdc1
2 8 49 2 active sync /dev/sdd1
4 8 65 3 active sync /dev/sde1
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Make the file system
You could also use LVM at this point.
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| $ sudo mkfs.ext4 /dev/md0
mke2fs 1.46.5 (30-Dec-2021)
Creating filesystem with 25152000 4k blocks and 6291456 inodes
Filesystem UUID: 3afba9e8-a786-47d2-820a-1ee88f8340b1
Superblock backups stored on blocks:
32768, 98304, 163840, 229376, 294912, 819200, 884736, 1605632, 2654208,
4096000, 7962624, 11239424, 20480000, 23887872
Allocating group tables: done
Writing inode tables: done
Creating journal (131072 blocks): done
Writing superblocks and filesystem accounting information: done
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Mount the raid array
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| sudo mount /dev/md0 /mnt/raid5
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Look at the new filesystem
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| $ df -h
Filesystem Size Used Avail Use% Mounted on
/dev/mapper/ubuntu--vg-ubuntu--lv 30G 4.7G 24G 17% /
/dev/sda2 2.0G 127M 1.7G 7% /boot
/dev/md0 94G 24K 90G 1% /mnt/raid5
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