I used Raspbian Buster Lite from here

i burned it on the microSD card using Rufus

then plugg your freshly burned SD card in the raspberry pi

power the pi using the micro USB.

connect a screen and a USB keyboard (or setup ssh directly by adding a empty file called ssh in the boot partition of the sd card)

1) enable ssh with raspi-config under interfacing option

2) setup the keyboard layout using raspi-config

3) change the password using again raspi-config

4) set hostname with raspi-config

5) setup a static ip adress by edditing /etc/dhcpd.conf

6) login via ssh and create.ssh

7) put your public key in .ssh/authorized_keys

8) sudo apt update && sudo apt upgrade -y

9) sudo reboot now

now your pi is ready

The objective is to have a safer way of storing the datas and a bigger storage than what the pi can offer with the SD card alone

sudo apt-get install mdadm

sudo dd if=/dev/zero of=/dev/sda bs=256M count=1

sudo dd if=/dev/zero of=/dev/sdb bs=256M count=1

(be careful. this wipe the content of your stick)

sudo parted /dev/sda
        mklabel gpt
        print
        mkpart primary 0% 100%
        print
        quit

sudo parted /dev/sdb
        mklabel gpt
        print
        mkpart primary 0% 100%
        print
        quit

sudo mdadm --create --verbose /dev/md0 --level=mirror --raid-devices=2 /dev/sda1 /dev/sdb1

sudo -i                (it dont work with sudo for some reason)
mdadm --detail --scan >> /etc/mdadm/mdadm.conf
exit

sudo mkfs.ext4 -v -m .1 -b 4096 -E stride=32,stripe-width=64 /dev/md0

sudo mount /dev/md0 /mnt
sudo chmod -R 777 /mnt

sudo df -h

if you loose a drive due to weak power supply, you can re-add it with : 

mdadm /dev/md0 -a /dev/sdX0

then edit the max_usb_current=1 in /boot/config.txt

sudo nano /boot/config.txt 
max_usb_current=1

you should now see youre raid

sudo blkid

note hte id of your RAID

sudo nano /etc/fstab

add the followinf line (replace X with your id) : 

UUID=XXXXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXXX /mnt ext4 defaults 0 0

sudo reboot now

once rebooted you should now see your raid mount in /mnt

sudo df -h

This step is optional but greatly recommand to extend the lifetime of your server.

cd /home/pi

sudo apt-get install git lsof mdadm -y git

git clone https://github.com/azlux/log2ram.git

cd log2ram

chmod +x install.sh

sudo ./install.sh

sudo nano /etc/log2ram.conf

set size  the buffer size from 40 to 128 megabyte

sudo reboot now

sudo apt-get install mariadb-server mariadb-client -y

sudo apt-get install mariadb-server mariadb-client -y

sudo apt-get install apache2 php libapache2-mod-php -y

sudo apt-get install phpmyadmin -y

sudo apt-get install php7.3-mysqlnd -y

sudo apt-get install php7.3-gd php7.3-dev php7.3-curl php7.3-mbstring php7.3-apcu php7.3 -y

sudo mkdir /mnt/phabFolder
sudo ln -s /mnt/phabFolder /var/www/phabFolder 

cd /var/www/phabFolder

sudo git clone https://github.com/phacility/libphutil.git  

sudo git clone https://github.com/phacility/arcanist.git

sudo git clone https://github.com/phacility/phabricator.git

sudo a2enmod rewrite

sudo a2enmod ssl

sudo systemctl restart apache2

sudo nano /etc/apache2/sites-available/phabricator.conf

<virtualhost *:80>
        ServerName '192.168.10.100'
        DocumentRoot /var/www/phabFolder/phabricator/webroot
        RewriteEngine on
        RewriteRule ^/rsrc/(.*)     -                       [L,QSA]
        RewriteRule ^/favicon.ico   -                       [L,QSA]
        RewriteRule ^(.*)$          /index.php?__path__=$1  [B,L,QSA]
        <Directory "/var/www/phabFolder/phabricator/webroot">
                Options FollowSymLinks
                Order allow,deny
                Allow from all
        </directory>
</virtualhost>

sudo a2ensite phabricator.conf

sudo systemctl reload apache2

sudo a2enmod rewrite

cd /var/www/phabFolder/phabricator/

sudo mysql
create user admin@localhost identified by 'yourPassword';

GRANT ALL PRIVILEGES ON *.* TO 'admin'@'localhost';

exit;

sudo ./bin/config set mysql.host localhost 

sudo ./bin/config set mysql.port 3306

sudo ./bin/config set mysql.user admin

sudo ./bin/config set mysql.pass 'yourPassword'

sudo ./bin/storage upgrade --user admin --password 'yourPassword' --force

sudo systemctl restart mysql
sudo systemctl restart apache2

sudo reboot now

wait a 45 secondes

From now your should see the phabricator webpage when you open  your raspberry pi adress using a web browser

lets start with the database : 

sudo systemctl stop mysql

sudo cp -R -p /var/lib/mysql /mnt/mysql

sudo chmod -R 777 /mnt/mysql

sudo nano /etc/mysql/mariadb.conf.d/50-server.cnf

 set datadir = /mnt/mysql

sudo systemctl start mysql

now for the repos

sudo mkdir /mnt/repo

sudo chmod 777 /mnt/repo

sudo ln -s /mnt/repo /var/repo

now you need to setup a admin password.

first login on phabricator using you broswer

then on the raspberry pi enter :

cd /var/www/phabFolder/phabricator/

bin/auth recover admin

you should get a link that allow to (re)set the password.

normally phabricator send you a mail with this link but it need to you to setup a mail server and i dont need a mail server just to send login link so for every new user that create an account you just need to run theses two command (replace admin with the username) and setup them a password