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Conference smurf::ase

Title:ase
Moderator:SMURF::GROSSO
Created:Thu Jul 29 1993
Last Modified:Fri Jun 06 1997
Last Successful Update:Fri Jun 06 1997
Number of topics:2114
Total number of notes:7347

1870.0. "SCSI/Fibrechannel support (DWZGA) ..." by RTOEU::KPLUSZYNSKI (Arrived...) Fri Feb 07 1997 10:24

    (When) will ASE support the soon-to-be-announced DWZGA 
    SCSI-to-Fibrechannel converter ?
    
    Thanks,
    
    Klaus
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1870.1BACHUS::DEVOSManu Devos DEC/SI Brussels 856-7539Fri Feb 07 1997 12:338
    Hi,
    
    My personal and humble opinion is : Never.
    
    The SCSI extenders are indeed not able to distinguish between a broken
    SCSI and a partition.
    
    Regards, Manu.
1870.2more infor?USCTR1::ASCHERDave AscherSat Feb 08 1997 12:5018
    Manu,
    
    Could you please clarify? If you have a config like
    
    
    >>>SCSI >>>>FIBER >>>> SCSI >>>>>>>
     |                           |     |   
    nodeA                        |  nodeB
                                SCSI device
    
    what would be the issue?  I can imagine that if some disks
    were on the left side of the fiber in the same place as nodeA
    and others were on the right side there is a potential issue
    - but that should be an illegal configuration rather than a
    show stopper.
    
    d
1870.3KITCHE::schottEric R. Schott USG Product ManagementSat Feb 08 1997 14:4215
The issue is that when a normal scsi bus fails, both sides an error.
When the extender fails, both sides may not see the
same failure (or even an error except for timeout)...

In short, the extender changes some of the properties of the scsi
bus, that will cause problems with the detection mechanisms in
ASE.  Thus it will not be supported.

If you are looking for DT solutions, see

http://www-unix.zk3.dec.com/www/clusters.html under Disaster Tolerance.

regards

Eric
1870.4Eric is closeFIEVEL::FILGATEBruce Filgate SHR3-2/W4 237-6452Sun Feb 16 1997 15:5522
 SCSI bus' can not tell the difference between a broken
 bus and a partition.  ASE clusters solved this problem by also
 keeping track of another communication path, network.

 While ASE remains in a small computer room, there is a small
 exposure to a double communication error, SCSI plus network,
 being evaluated incorrectly and generating a partition that 
 destroys the customer data.  The probability is non-zero,
 but accepted as being small enough by the engineers responsible
 for ASE design.

 If ASE were to be extended beyond the computer room, this small
 probability grows as the interconnect distance increases.  The
 engineering that was done for computer room hazard protection,
 is entirely inadequate for the longer distances that FC enables.

 Until the design engineers in ASE INVENT a solution to this large
 area partition issue, there will not be a fully supported ASE that
 won't corrupt customer data with a long haul FC.

 Bruce