Library /sys$common/syshlp/sysmanhelp.hlb IO, FIND_WWID, Description  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    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 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 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 IO FIND_WWID is to populate the
    SYS$DEVICES.DAT file, you need to invoke the IO FIND_WWID command
    only one time for each new device. Note that using the 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
    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. (IO FIND_WWID
    does not load or connect the actual device drivers.)

                                   NOTE

       A restriction exists in OpenVMS Version 7.3: 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 IO FIND_WWID command again, to append the new
       device information to the SYS$DEVICES.DAT file.

    In an OpenVMS cluster environment, you must run the IO FIND_
    WWID command on each node in the cluster to update various data
    structures in memory. Alternatively, you can run 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$DEVICES.DAT file are kept consistent,
    preferably by running the IO FIND_WWID command on all nodes.
    Alternatively, you can run IO FIND_WWID to update just one
    SYS$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.

    Compaq 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.