VMS Help MOUNT, Qualifiers, /AUTOMATIC  *Conan The Librarian (sorry for the slow response - running on an old VAX)

       /AUTOMATIC (default)
       /NOAUTOMATIC

    Determines whether MOUNT enables or disables automatic volume
    switching and labeling for magnetic tape or ISO 9660 CD-ROM.

    Magnetic Tape

    If you have multiple magnetic tape drives allocated to a volume
    set, the magnetic tape ancillary control process (MTACP) performs
    the volume switch by sequentially selecting the next available
    drive allocated to the volume set. The MTACP expects the next
    reel of the volume set to be loaded on that drive.

    If the MTACP is writing to the volume set, it creates a label and
    initializes the magnetic tape with that label and the protections
    established for the first magnetic tape of the volume set. If it
    is reading from the volume set, the MTACP generates the label and
    attempts to mount the next magnetic tape with that label. If the
    drive has the wrong magnetic tape (or no magnetic tape) loaded,
    the MTACP sends a message to the operator's console to prompt for
    the correct magnetic tape.

    The label generated by the MTACP fills the 6-character volume
    identifier field. The first four characters of the field contain
    the first four characters of the label specified in the MOUNT
    command, padded with underscores when the label is not at least
    four characters. The fifth and sixth characters contain the
    relative volume number for this reel in the volume set.

    If you specify /NOAUTOMATIC, the MTACP requires operator
    intervention to switch to the next drive during end-of-tape
    processing, and requires that the operator specify a label for
    each new reel added to a volume set.

    ISO 9660 CD-ROM

    Under ISO 9660, not all volume-set members must be mounted to
    perform I/O operations against that volume set. By default, if
    I/O operations attempt to access an unmounted volume-set member,
    an operator message is sent to all DISK CLASS operators for
    system-mounted volume sets, or the owning process for privately
    mounted volume sets. The message specifies the volume-set member
    to mount to complete the I/O operation requested. If /NOAUTOMATIC
    is specified, then an I/O operation to a nonmounted volume set
    member completes with an error message SS$_DEVNOTMOUNT.

    Example

    The following command instructs MOUNT not to generate its own
    label for the second volume, but to use the ones supplied with
    the MOUNT command instead. If the second volume is not already
    labeled, then the operator must use REPLY/INIT and supply the
    second label.

    $ MOUNT/NOAUTOMATIC MTA0: ABCD,EFGH