/STRUCTURE=level

    Specifies whether the volume should be formatted in Files-11
    On-Disk Structure Level 1, 2 (the default), or 5.

    Structure Level 1 is incompatible with the /DATA_CHECK and
    /CLUSTER_SIZE qualifiers. The default protection for a Structure
    Level 1 disk is full access to system, owner, and group, and read
    (R) access to all other users.

    Note that Alpha does not support ODS-1 disks, and specifying 1 on
    Alpha results in an error.

    See the VSI OpenVMS System Manager's Manual, Volume 1: Essentials
    for more information about ODS-5 disks.