Upon successful completion, mrd_ready(3mrd) will return MRD_
    STATUS_SUCCESS. On a failure, one of the following status values
    will be returned.

1  –  MRD_STATUS_PARAM

    This error is returned if the robot_info or dev_status arguments
    are NULL pointers.

2  –  MRD_STATUS_ROBOT_ILLEGAL_REQUEST

    This error occurs when the medium changer does not support the
    Ready Inport command. The TL820 family of DLT libraries support
    this command. The TL810 family of DLT libraries allows this
    command to succeed, but it doesn't perform any function.

    It is also used for a SCSI command failure, when the ASC is set
    to one of:

    o  0x1A - Parameter list length error

    o  0x20 - Invalid command operation code

    o  0x22 - Unsupported command

    o  0x24 - Illegal field in CDB

    o  0x25 - Logical unit not supported

    o  0x26 - Threshold parameters not supported

    o  0x28 - Import or Export element accessed

    o  0x2C - Command sequence error

    o  0x39 - Saving parameters not supported

    o  0x3D - Invalid bits in Identify message

    o  0x53 - Medium removal prevented

    This status is also returned when the ASC and ASCQ are zero, but
    the key is five (5).

3  –  MRD_STATUS_IVCHAN

    This error code is used when an OpenVMS system service fails
    with the status SS$_IVCHAN. It is likely when an operating system
    specific routine is used on a device that hasn't been opened by
    mrd_startup(3mrd).