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    RE: IPS Issues document



    
    
    Hi,
    
    Good job.  I had only an hour to glance over it so I might come later with
    some more but here are some observations:
    
       Performance - has two aspects - related but not entirely equivalent -
       latency and bandwidth. It is obvious that bandwidth is not a
       differentiating factor for any type of interconnect as they use the same
       physical infrastructure in a similar fashion. Latency on the other hand
       is a more difficult factor as it relates to hardware, software and
       protocol. CPU utilization by itself is arguably not a limiting factor -
       as it can be solved by simply adding more CPUs or waiting until the CPUs
       get faster.  All the elements you mention under CPU utilization refer
       mostly to the memory subsystem utilization - and there are no known ways
       to improve on that  as the memory does not get faster as fast as the
       CPUs do (no Moore law for DRAMs!).  Protocol stack processing reduction
       is the mainly improving your "placement" techniques and reducing copy
       operations. Storage subsystems fare better (and so does FCP) since the
       do scatter-gather DMA (and DMA is times faster than copy due to an
       architectural "feature" of DRAMs that use one address setup for several
       memory operations.  This is the reason why we think that giving the
       protocols a chance to do well DMA is so important
       Adoption of the solution by the device vendors is important but not
       critical. Adoption of a "last half-meter" protocol - like the serial-ATA
       pushed by Intel, with all its drawbacks could offer a cheap alternative
       for fiercely competitive environments like desktops with SCSI as a more
       robust and functional cousin. For clusters and RAIDs both can be
       considered and with IP getting adopted by pervasive computing may get IP
       networks to the point at which the price differential will not exist
       anymore
       You do not mention the SBP although, I recall it as the first serial
       SCSI standardized
       On the performance section I think that solution scalability for the
       low-end to the high-end is essential as it is the only way to gain
       "mass" and survive the continuous shift in performance
       Management should include both storage and interconnect.  Any solution
       should be able to use for interconnect management whatever is good for
       network management with only slight concern about the device specifics.
       A factor that I have difficulty expressing is - skills and tools
       availability. By this I mean planers, administrators and (why not!) even
       salesman and their tools. Any solution that we leverage an existing
       skill (and tools) base will have a distinct advantage
    
    Regards,
    Julo
    
    Julian Satran - IBM Research at Haifa
    
    


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Last updated: Tue Sep 04 01:08:17 2001
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