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    SubjectRe: scsi disk detection and /dev names, RE: My $.02 on the raging de vfs debate
    On 11 Oct 1999, H. Peter Anvin wrote:

    1. PCI bus numbers are fairly volatile; they are assigned sequentially
    by a depth-first search. Inserting a multiport Ethernet card
    (which usually have PCI-PCI bridges onboard) could move a whole lot
    of bus numbers for you. Same thing with SCSI controller numbers.

    in that case we should consider not including PCI location. ie let
    controllers continue to be autodetected, but describe
    devices/functions of them according to location. I think this would
    suit scsi and busses quite well.

    2. Consider if location-basis is really what you want, and if so, if
    it really matters. Rearranging your SCSI busses, for example, is
    probably quite common. On busses where you have device serial
    numbers, or for disks where you have labels, it probably would
    provide a better basis.

    true. though i think in the case of scsi 90+% of the time the change
    is a disk swapped or added (eg hardware failure or pressing need for
    expansion). Re-arranging busses / controllers might imply a planned
    rebuild.

    In the former case there's a good chance admin is stressed, :), so
    unambigous device names would be nice, to avoid confusion.

    In the second case you know the hardware well enough, and just need
    to watch the boot messages to watch for controller detection. Then
    you'll know "this device has to be /dev/controllerXdeviceYfunctionZ".

    You don't have to remember the order of detection of individual
    devices - which you would with what we have now. And new hardware
    config is when you have least familiarity with detection order, but
    most with physical location.

    3. Solaris seems to teach the lesson that if you make the device names
    too complex, noone will use them. Solaris has a very complete
    location-based device naming scheme, but I know very few Solaris
    administrators who use those names, as opposed to the short
    symlinks.

    So we'll just have to show more imagination than Sun! :) The solaris
    PCI based names are a bit cumbersome, i agree.

    -hpa

    regards,
    --
    Paul Jakma paul@clubi.ie
    PGP5 key: http://www.clubi.ie/jakma/publickey.txt
    -------------------------------------------
    Fortune:
    The only difference between a car salesman and a computer salesman is
    that the car salesman knows he's lying.


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