HP OpenVMS Systems

CI Bandwidth, I/O rate?

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The Question is:

 
What is the maximum number of I/O's per second on a CI?
 

The Answer is :

 
  The CI bandwidth is 70 megabits per second, dual channel.  This
  is 17.5 megabytes per second raw bandwidth.  (For comparision
  purposes, fast-wide SCSI is 20 megabytes per second raw bandwidth.)
 
  The expected I/O rate depends on other factors, not the least
  of which are other CI activity, the type(s) of CI controller(s),
  the host activity level, and the size of the particular I/O.
 
  CI adapters have significantly lower CPU overhead per operation
  than SCSI, due to the adapter itself.  While this does not alter
  the peak bandwidth, it can become a factor when you are either
  CPU limited or are performing hundreds or thousands of I/Os per
  second.
 
  CIPCA CI controllers have been measured at roughly 16 megabytes per
  second using larger I/O sizes and MSCP traffic protocols.  Smaller
  transfers will reduce the bandwidth, but I/O rates of well over 4000
  I/Os per second have been measured on CIPCA controllers.  For the
  purposes of comparision, a KZPSA SCSI controller can operate at
  roughly 13 megabytes per second with larger I/O sizes (and higher
  CPU overhead).
 
  To determine how much CI traffic a host is involved with, you can
  use tools such as SHOW CLUSTER and DECamds to monitor the current
  bandwidth at each particular host.  There is no particularly easy
  way to measure the aggregate bandwidth directly on the CI.
 

  

     

     
answer written or last revised on ( 3-MAR-2000 )
     
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