I've created a 3 disk RAID5 array using mdadm/LVM, which contained a few files to demonstrate how data is striped across an array.
How it was created;
Create file of a fixed size, using a unique string/word which is easily identifiable such as 'APPLE'
The 'yes' command will output the string passed to it (APPLE) continually until killed. It's piped into head, and it'll output a file of a size of 1GB which is redirected to apple.txt
$ yes APPLE | head -c 1073741824 > apple.txt
Do this 3 more times using banana, carrot, date, eggplant, to produce 5 x 1GB text files.
Create 3 x 2GB volumes, attach to virtual machine.
Unwilling to restart the virtual machine, I probed the SCSI host to detect new disks.
$ for host in /sys/class/scsi_host/*; do echo "- - -" | sudo tee $host/scan; ls /dev/sd* ; done
$ lsblk
NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINTS
sda 8:0 0 2G 0 disk
sdb 8:16 0 80G 0 disk
├─sdb1 8:17 0 1M 0 part
├─sdb2 8:18 0 513M 0 part /boot/efi
└─sdb3 8:19 0 79.5G 0 part /
sdc 8:32 0 2G 0 disk
sdd 8:48 0 2G 0 disk
So we have sda, sdc, and sdd.
Create RAID5 volume using mdadm
$ mdadm --create --verbose /dev/md0 --level=5 --raid-devices=3 /dev/sda /dev/sdc /dev/sdd
mdadm: layout defaults to left-symmetric
mdadm: layout defaults to left-symmetric
mdadm: chunk size defaults to 512K
mdadm: size set to 2094080K
mdadm: Defaulting to version 1.2 metadata
mdadm: array /dev/md0 started.
Check block device output prior to creating filesystem
$ lsblk
NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINTS
sda 8:0 0 2G 0 disk
└─md0 9:0 0 4G 0 raid5
sdb 8:16 0 80G 0 disk
├─sdb1 8:17 0 1M 0 part
├─sdb2 8:18 0 513M 0 part /boot/efi
└─sdb3 8:19 0 79.5G 0 part /
sdc 8:32 0 2G 0 disk
└─md0 9:0 0 4G 0 raid5
sdd 8:48 0 2G 0 disk
└─md0 9:0 0 4G 0 raid5
sr0 11:0 1 1024M 0 rom
$ fdisk -l /dev/md0
Disk /dev/md0: 3.99 GiB, 4288675840 bytes, 8376320 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 524288 bytes / 1048576 bytes
Create ext4 filesystem on /dev/md0
$ mkfs.ext4 /dev/md0
mke2fs 1.46.5 (30-Dec-2021)
Creating filesystem with 1047040 4k blocks and 262144 inodes
Filesystem UUID: 63a60555-ea65-4ed4-83f7-e7e851db8f52
Superblock backups stored on blocks:
32768, 98304, 163840, 229376, 294912, 819200, 884736
Allocating group tables: done
Writing inode tables: done
Creating journal (16384 blocks): done
Writing superblocks and filesystem accounting information: done
Mount volume to /mnt/iblue5 and copy dummy data to it (attempted to copy all 5 x 1GB files, which partially failed due to insufficient space).
$ mkdir /mnt/iblue5
$ mount /dev/mapper/data-iblue /mnt/iblue5
$ ls /mnt/iblue5
lost+found
$ cp /home/user/Desktop/*.txt /mnt/iblue5/
$ ls -lah /mnt/iblue5
total 3.9G
drwxr-xr-x 3 root root 4.0K Dec 9 22:39 .
drwxr-xr-x 17 root root 4.0K Dec 9 22:25 ..
-rw-r--r-- 1 root root 1.0G Dec 9 22:38 apple.txt
-rw-r--r-- 1 root root 1.0G Dec 9 22:38 banana.txt
-rw-r--r-- 1 root root 1.0G Dec 9 22:39 carrot.txt
-rw-r--r-- 1 root root 858M Dec 9 22:39 date.txt
-rw-r--r-- 1 root root 0 Dec 9 22:39 eggplant.txt
drwx------ 2 root root 16K Dec 9 22:37 lost+found
