From: Bruce Allen <ballen@gravity.phys.uwm.edu>
Subject: slow NFS performance extracting bits from large files
Date: Mon, 16 Dec 2002 01:02:55 -0600 (CST)
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Message-ID: <Pine.GSO.4.21.0212160054001.4121-100000@dirac.phys.uwm.edu>
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Cc: Bruce Allen <ballen@gravity.phys.uwm.edu>
To: nfs@lists.sourceforge.net
Errors-To: nfs-admin@lists.sourceforge.net

I've searched/browsed the mail archive and the online documentation but am
still a bit clueless about where to start.

I am working on a scientific data analysis application which needs to
extract a little bit of data from around 10,000 files.  The files
themselves are each around 1 MB in size. The application does:

for (i=0; i<10000; i++){
  open() ith file
  read() 32 bytes from beginning
  lseek() to somewhere in the middle of the file
  read() 620 bytes from the middle of the file
  close() ith file
}

If I run this with the data set on a local disk, the total run time is
around 1 sec -- very reasonable since I am transferring around 6 MB of
data.

If I run this on an NFS-mounted disk the performance is 100 times worse.
Both client and server are stock RH 7.3.  Note that if I run it a second
time, when the data is presumably cached, it takes just a few seconds to
run.

Is it obvious what needs to be changed/tuned to improve this performance?
Or if not, could someone suggest a tool and a strategy for tracing down
the cause of the poor performance?

Sincerely,
	Bruce Allen


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