( THIS IS DISCUSSION ONLY - NOT VERIFIED OR ENDORSED - USE AT YOUR OWN RISK )
After creating a z1d.large instance you need to mount the volume otherwise you will only see 8 GB (https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/ebs-using-volumes.html). These commands will mount the volume under the folder where the maps are stored:
sudo mkfs -t xfs /dev/nvme0n1 sudo mount /dev/nvme0n1 /tmp/workshop/7777/content/555160 sudo chown -R steam /tmp/workshop/7777/content/555160 sudo chgrp -R steam /tmp/workshop/7777/content/555160
Warning: This volume is only preserved for the time the instance is running.