ITEM: D7323L

What are the parameters for an Async I/O system.

Question:

I have an 970 RISC with AIX level 3.2.3e and I am trying to set up an
Async I/O.  I have looked in info-explorer  and other places.  I want
to find out what the reasonable limits and the effects on memory of
various settings

Response:

There are no "reasonable limits" established for the aio daemon.
However, there are some implementation guidelines I have developed
during my use of AIO:

1.  If there are LARGE numbers of programs/users/processes that wish
    to use AIO, then increase the number of daemons AND reduce the 
    number of requests each daemon will service.  This increases 
    the number of IO starts, while limiting the amount of memory 
    the daemons consume.

2.  When tuning the system for performance while using AIO, monitor
    the paging and memory systems for an increase in or unexpected 
    paging activity.  If paging has become more prevalent, reduce 
    the number of daemons, or decrease the number of IO's each 
    daemon will service.

3.  FOR EACH AIO there are 2 copies of the data being read/written:
    a.  The copy the user has in their private data space and
    b.  The copy the AIO daemon receives ...

4.  It is always best to start with one daemon and a modest number of
    IO's and increase either parameter ONE AT A TIME while watching
    for changes in system memory consumption and/or paging.



Support Line: What are the parameters for an Async I/O system. ITEM: D7323L

Dated: October 1993 Category: N/A

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