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. StackOverFlow question - https://stackoverflow.com/questions/53162620/automate-gcp-persistent-disk-initialization

gcp_compute_mount_persistent_disk.sh

#!/bin/bash
set -euxo pipefail

MNT_DIR=/mnt/disks/persistent_storage

if [[ -d "$MNT_DIR" ]]; 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_DIR
        sudo mount -o discard,defaults /dev/sdb $MNT_DIR

        # Add fstab entry
        echo UUID=`sudo blkid -s UUID -o value /dev/sdb` $MNT_DIR ext4 discard,defaults,nofail 0 2 | sudo tee -a /etc/fstab
fi