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Calculating Buffered I/O Rates?

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The Question is:

When I monitor the buffered I/O rate using the OpenVMS Monitor utility, I see
 buffered I/O rates of about 9000 buffered I/Os per second, but when I use
 either AMDS or Availability Manager, I see values of about 900.
Which one do I believe, or how can I get an accurate figure?

The Answer is :

  Using ANALYZE/SYSTEM, EXAMINE the system data cell PMS$GL_BUFIO, then
  wait a known number of seconds (eg: 10), then re-examine the same cell.
  Subtract the first value seen from the second, and then divide that by
  the interval between the two EXAMINE commands.  The result will be your
  buffered I/O rate, per second.
  For the system-wide direct I/O value, examine PMS$GL_DIRIO.
  For alternatives, please see the sys$getrmi system service (on OpenVMS
  V7.3 and later), and also consider researching the (undocumented and
  unsupported) exe$getspi call.
  As for the differences between MONITOR and AMDS, that would clearly
  appear to be either a bug or a misinterpretation of a display, though
  whether this problem is within AMDS or MONITOR or elsehwere is unclear.

answer written or last revised on ( 31-JUL-2002 )

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