raid10 combines the speed of raid0 with the resilience of raid1.

watch out: shingled hdd are not good for RAID!

setup of GNU Linux mdadm software RAID10 is actually pretty straight forward: no need to do any partitioning.

# tested on
hostnamectl;
  Operating System: Debian GNU/Linux 11 (bullseye)
            Kernel: Linux 5.10.0-8-amd64
      Architecture: x86-64

su - root;
# hardware requirement: 4x identical 4 TB harddisks
# (e.g. Hitachi HGST Ultrastar 7K4000)
lsblk 
NAME   MAJ:MIN RM   SIZE RO TYPE   MOUNTPOINT
sda      8:0    0   3.6T  0 disk   
sdb      8:16   0   3.6T  0 disk   
sdc      8:32   0   3.6T  0 disk   
sdd      8:48   0   3.6T  0 disk   

apt update
# needed
apt install mdadm
# optional
apt install lm-sensors hddtemp smartmontools
systemctl start smartd
/etc/init.d/kmod start
# optional: keep an eye on cpu & hd temps
sensors-detect
# YES, YES, YES....

# script that runs a bunch of health tests and shows temp of all harddisks

cat /scripts/harddisk_iteration.sh
#!/bin/bash

echo "=== iterate over all harddisks in the system: ==="
for x in {a..z}
do
if test $(ls /dev |grep sd$x |wc -l) != 0; then
	echo "===== /dev/sd$sd$x =====";
        hddtemp /dev/sd$sd$x
        if smartctl -l scterc,70,70 /dev/sd$sd$x > /dev/null ; then echo "is good for raid (not shingled)"; else echo "no good for raid, shingled harddisk, sue vendor"; fi;
        smartctl -l error /dev/sd$sd$x;
        echo "";
	smartctl -H /dev/sd$sd$x;
fi
done

# make mount point
mkdir /media/user/md0

mdadm --create /dev/md0 --level=10 --raid-devices=4 /dev/sd[a-d]

# watch temps of sensors while raid builds
watch -n 2 'cat /proc/mdstat; sensors'

# when raid build is complete
# format and label it
mkfs.ext4 -L "raid10" /dev/md0

# mount it
mount /dev/md0 /media/user/md0

# so non-root-user can actually access and use it
chown -R user: /media/user/md0

# :) run a basic harddisk benchmark

cat /scripts/bench/bench_harddisk.sh 
#!/bin/bash
echo "=== harddisk sequential write and read bench v1 ==="
echo "starting test on the device that holds the current directory the user is in"
echo "no need to run it as root"
echo ""
echo "========== writing 3GB of zeroes =========="
time dd if=/dev/zero of=./testfile bs=3G count=1 oflag=direct

echo "========== reading 6GB of zeroes =========="
time dd if=./testfile bs=3GB count=1 of=/dev/null

echo "========== tidy up remove testfile =========="
rm -rf ./testfile;

# run sequential write/read benchmark
cd /media/user/md0
time /scripts/bench/bench_harddisk.sh 
=== harddisk sequential write and read bench v1 ===
starting test on the device that holds the current directory the user is in
no need to run it as root

========== writing 3GB of zeroes ==========
0+1 records in
0+1 records out
2147479552 bytes (2.1 GB, 2.0 GiB) copied, 13.3767 s, 161 MB/s

real	0m13.393s
user	0m0.000s
sys	0m2.464s
========== reading 6GB of zeroes ==========
0+1 records in
0+1 records out
2147479552 bytes (2.1 GB, 2.0 GiB) copied, 8.1213 s, 264 MB/s

real	0m8.129s
user	0m0.000s
sys	0m1.487s
========== tidy up remove testfile ==========

real	0m21.641s
user	0m0.002s
sys	0m4.068s

# another python based harddisk benchmark
# which tests handling of small files
# for whatever reason wants to run as root (actually no good)
time /scripts/bench/bench_harddisk_small_files.py 

create test folder:
0.00346207618713
sh: 1: sudo: not found

create files:
9.60848593712
sh: 1: sudo: not found

rewrite files:
1.95726704597
sh: 1: sudo: not found

read linear:
0.54031085968
sh: 1: sudo: not found

read random:
0.626809120178
sh: 1: sudo: not found

delete all files:
3.57898211479
sh: 1: sudo: not found

real	0m16.336s <- that is pretty quick actually (compared to kingston ssd + i5)
user	0m3.537s
sys	0m11.636s

echo "=== print nice overview over all harddisks and filesystems: ==="
lsblk -o "NAME,MAJ:MIN,RM,SIZE,RO,FSTYPE,MOUNTPOINT,UUID"

=== print nice overview over all harddisks and filesystems: ===
NAME   MAJ:MIN RM   SIZE RO FSTYPE            MOUNTPOINT          UUID
sda      8:0    0   3.6T  0 linux_raid_member                     0816d6e1-be69-1f26-fac6-xxxxxxxxxxxx
└─md0    9:0    0   7.3T  0 ext4              /media/user/md0     25eec7f4-304c-4dfa-862b-xxxxxxxxxxxx
sdb      8:16   0   3.6T  0 linux_raid_member                     0816d6e1-be69-1f26-fac6-xxxxxxxxxxxx
└─md0    9:0    0   7.3T  0 ext4              /media/user/md0     25eec7f4-304c-4dfa-862b-xxxxxxxxxxxx
sdc      8:32   0   3.6T  0 linux_raid_member                     0816d6e1-be69-1f26-fac6-xxxxxxxxxxxx
└─md0    9:0    0   7.3T  0 ext4              /media/user/md0     25eec7f4-304c-4dfa-862b-xxxxxxxxxxxx
sdd      8:48   0   3.6T  0 linux_raid_member                     0816d6e1-be69-1f26-fac6-xxxxxxxxxxxx
└─md0    9:0    0   7.3T  0 ext4              /media/user/md0     25eec7f4-304c-4dfa-862b-xxxxxxxxxxxx
# note that of the 4x 4TB RAID10 not 8TB but 7.3TB can be used (-8.75%)
# :) 
# congratz! :)
# do 10sec of the happy dance! :)

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