ECS Container Mount Mode Z or ""

Running Grafana with Compose makes all my three mounts to be as "Mode": "rw", but once I run it on ECS with EC2 type, I get "Mode": "z" and "Mode": "". What does z mean?

"Mounts": [
    {
        "Type": "volume",
        "Name": "dev_grafana_data",
        "Source": "/var/lib/docker/volumes/dev_grafana_data/_data",
        "Destination": "/var/lib/grafana",
        "Driver": "local",
        "Mode": "z",
        "RW": true,
        "Propagation": ""
    },
    {
        "Type": "bind",
        "Source": "/opt/grafana/grafana/provisioning",
        "Destination": "/etc/grafana/provisioning",
        "Mode": "",
        "RW": true,
        "Propagation": "rprivate"
    },
    {
        "Type": "bind",
        "Source": "/opt/grafana/grafana/conf",
        "Destination": "/etc/grafana/conf",
        "Mode": "",
        "RW": true,
        "Propagation": "rprivate"
    }
]