Prior to configuring a tape device on Fibre Channel ports, the
    worldwide identifier (WWID) of the device must be detected
    and stored, along with a device name, in the text file
    SYS$SYSTEM:SYS$DEVICES.DAT. You use the SYSMAN command IO FIND_
    WWID to accomplish this.

    The SYSMAN IO FIND_WWID command probes all Fibre Channel ports
    and locates all tape and medium changer devices. For tapes and
    medium changers that have not been detected by any previous
    SYSMAN IO FIND_WWID command, IO FIND_WWID assigns a device name,
    retrieves the WWID of the device, stores the device name and WWID
    data in the SYS$SYSTEM:SYS$DEVICES.DAT file, and updates memory
    structures.

    Because the main goal of SYSMAN IO FIND_WWID is to populate the
    SYS$DEVICES.DAT file, you need to invoke the SYSMAN IO FIND_
    WWID command only one time for each new device. Note that using
    the SYSMAN IO FIND_WWID command for the first time detects all
    existing tape and medium changer devices on the system at that
    time.

    Once the information is stored in the file, subsequent use of
    the SYSMAN IO AUTOCONFIGURE command reads the file and configures
    the tape and medium changer devices automatically, loading or
    connecting the device drivers as needed. The SYS$DEVICES.DAT
    file is read during each system reboot, initiating the automatic
    configuration of tapes and medium changers on the Fibre Channel.
    (SYSMAN IO FIND_WWID does not load or connect the actual device
    drivers.)

                                   NOTE

       If you add more devices to the system at a later time,
       you must powercycle the MDR to update internal mapping
       information. You must also run the SYSMAN IO FIND_WWID
       command again to append the new device information to the
       SYS$DEVICES.DAT file.

       Similarly, for the Network Storage Router (NSR), the LUN map
       must be updated.

    In an OpenVMS cluster environment, you must run the SYSMAN IO
    FIND_WWID command on each node in the cluster to update various
    data structures in memory. Alternatively, you can run SYSMAN
    IO FIND_WWID on one node, and then reboot the other nodes that
    share that same system disk, because the SYS$DEVICES.DAT file is
    read at boot time and causes memory structures to be correctly
    initialized.

    In the case of multiple system disks in the cluster, ensure that
    all copies of the SYS$DEVICES.DAT file are kept consistent,
    preferably by running the SYSMAN IO FIND_WWID command on all
    nodes. Alternatively, you can run IO FIND_WWID to update just
    one SYS$DEVICES.DAT file, and then manually edit the remaining
    SYS$DEVICES.DAT files by cutting and pasting the appropriate
    devnam/WWID records from the original file to the target files.

    VSI recommends that you refrain from copying the entire original
    file to another system disk, because the SYS$DEVICES.DAT file
    is also used to define Port Allocation Classes, and PAC entries
    could be inadvertently transferred to the target system.