Master

    Allows you to explicitly state how drives should be used when
    they are to be accessed concurrently. This is a positional
    qualifier that designates a tape drive as a master tape drive.

    When the Master qualifier is used, it must be used on the first
    drive specified. All additional drives become slaves to that
    master until the end of the command line, or until the next
    Master qualifier, whichever comes first.

    If the Master qualifier is used on a drive that does not have
    an independent I/O path (not a hardware master), performance
    decreases.

    If the Master qualifier is not used, and concurrent tape access
    is requested (using the Volumes=n qualifier), RMU Restore uses
    the same automatic configuration procedure it employs with the
    backup operation to select the master drives.

    Using the Master qualifier is an error if you do not specify
    concurrent tape access (you do not specify the Volumes=n
    qualifier). See the description of the Volumes qualifier for
    further information on specifying concurrent tape access.