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20040526: asynchronous read ahead and write behind on NetCDF

Giang,

> To: address@hidden
> From: Giang Nong <address@hidden>
> Subject: read ahead and write behind on NetCDF
> Organization: GFDL/NOAA
> Keywords: 200405242114.i4OLENtK012695 netCDF

The above message contained the following:

> I use IRIX 6.5 and I want to try using netcdf_ffiospec. I want to use 
> asynchronous  read/write and I try the following setting:
> netcdf_ffiospec = cachea:256:8:2
>
> My question: is it enough to specify netcdf_ffiospec to get asynchronous I/O, 
> in other words, do I need to get into source code of NetCDF and make some 
> change there. In case I need to modify NetCDF source code, what changes are 
> necessary to get asynchronous I/O?

I'm afraid that you can't use the FFIO subsystem on a computer running 
IRIX because the FFIO subsystem is a feature of Cray (and Cray-like)
computers only.  The "ffio" module of the netCDF package was developed
to allow netCDF users on Cray systems to use the Cray FFIO subsystem
when accessing netCDF files.

The only other I/O subsystem within the netCDF package is the "posixio"
module.  This module uses simple POSIX read() and write() calls and
doesn't support asynchronous I/O.

Doing what you want would require the writing of a new I/O subsystem for
the netCDF package.  Regrettably, we don't have the resources to do that
at this time.

> Thank you very much.
> 
> Giang Nong
> GFDL/NOAA

Regards,
Steve Emmerson

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