Use the following script to mount a persistent storage during startup. This is helpful when you provision the compute instance as well as the persistent disk using some automation tool like Terraform.

gcp_compute_mount_persistent_disk.sh

#!/bin/bash
set -euxo pipefail

if [[ -d "/mnt/disks/persistent_storage" ]]; then
        exit
else 
        sudo mkfs.ext4 -m 0 -F -E lazy_itable_init=0,lazy_journal_init=0,discard /dev/sdb; \
        sudo mkdir -p /mnt/disks/persistent_storage
        sudo mount -o discard,defaults /dev/sdb /mnt/disks/persistent_storage
fi