This is how I did the pi raid.
I am using sda and sdb where each is formatted with an ext4 fs.
Used Raspberry Pi RAID NAS Server Setup and DigitalOcean's How To Create RAID Arrays with mdadm on Ubuntu 22.04
Partitioning during fdisk:
$ sudo fdisk /dev/sda[m] for help
[o]
[n]
[p]
[1]
[Enter]
[Enter]
[w]
sudo fdisk /dev/sda
sudo mkfs.ext4 /dev/sda1
sudo fdisk /dev/sdb
sudo mkfs.ext4 /dev/sdb1
sudo mdadm --create --verbose /dev/md0 --level=mirror --raid-devices=2 /dev/sda1 /dev/sdb1
cat /proc/mdstat
sudo -i
# insert the raid config
mdadm --detail --scan > /etc/mdadm/mdadm.conf
less /etc/mdadm/mdadm.conf
exit
sudo mkfs.ext4 -v -m .1 -b 4096 -E stride=32,stripe-width=64 /dev/md0
sudo mkdir /mnt/raid1
sudo mount /dev/md0 /mnt/raid1
# chmod my user in as owner
sudo chown user:user /mnt/raid1
sudo update-initramfs -u
# get the uuid for fstab
ls -l /dev/disk/by-uuid
sudo vi /etc/fstab
sudo hdparm -I /dev/md0
cat /proc/mdstat
# turn on monitor blank
sudo raspi-configfstab entry:
UUID=14c870f3-ae42-4c7d-ab06-0b45ed50048c /mnt/raid1 ext4 defaults,noatime 0 0
test performance
sudo apt install -y hdparm
sudo hdparm -I /dev/md0
sudo hdparm -tT --direct /dev/md0