Format device with two ext4 partitions of equal size

format.sh

#!/bin/bash

set -euo pipefail

if [ -z "${1:-}" ]; then
    echo "Usage: $0 <device>"
    echo "  e.g. $0 vdb"
    exit 1
fi

DEVICE="$1"
DISK="/dev/${DEVICE}"

if [ ! -b "$DISK" ]; then
    echo "Error: $DISK is not a block device"
    exit 1
fi

echo "Creating GPT label and two equal partitions on $DISK..."
sudo /sbin/parted -s "$DISK" mklabel gpt
sudo /sbin/parted -s "$DISK" mkpart primary ext4 0% 50%
sudo /sbin/parted -s "$DISK" mkpart primary ext4 50% 100%
sudo /sbin/partprobe "$DISK"

for i in 1 2; do
    PART="${DISK}${i}"

    # Wait for partition node to appear
    for attempt in $(seq 1 10); do
        [ -b "$PART" ] && break
        sleep 1
    done

    if [ ! -b "$PART" ]; then
        echo "Error: partition $PART did not appear"
        exit 1
    fi

    LABEL="${DEVICE}${i}"
    MOUNTPOINT="/mnt/${LABEL}"

    echo "Formatting $PART as ext4 with label $LABEL..."
    sudo mkfs.ext4 -F -L "$LABEL" "$PART"

    sudo mkdir -p "$MOUNTPOINT"
    UUID="$(sudo blkid -s UUID -o value "$PART")"
    echo "UUID=${UUID}  ${MOUNTPOINT}  ext4  defaults,nofail  0  2" | sudo tee -a /etc/fstab

    echo "Mounting $PART at $MOUNTPOINT..."
    sudo mount "$PART" "$MOUNTPOINT"
done

sudo mount -a
echo "Done. Both partitions of $DISK are mounted."