From: Trond Myklebust <trond.myklebust@fys.uio.no>
Subject: Re: async vs. sync
Date: Mon, 22 Nov 2004 17:20:42 -0500
Message-ID: <1101162043.11196.88.camel@lade.trondhjem.org>
References: <EXCHG20034NQhEP9w0z00007249@EXCHG2003.microtech-ks.com>
	 <41A25DCB.6020700@int-evry.fr>  <41A25FA3.6060000@int-evry.fr>
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Cc: Roger Heflin <rheflin@atipa.com>, Olaf Kirch <okir@suse.de>,
	nfs@lists.sourceforge.net
To: jehan procaccia <jehan.procaccia@int-evry.fr>
In-Reply-To: <41A25FA3.6060000@int-evry.fr>
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m=E5 den 22.11.2004 Klokka 22:52 (+0100) skreiv jehan procaccia:
> > [root@arvouin tmp]# mount cobra3:/p2v5f1 -o=20
> > async,wsize=3D32768,rsize=3D32768,soft /mnt/cobra3
> > [root@arvouin /mnt/cobra3/mci/test/Test-sync]
> > $time tar xvfz /usr/src/redhat/SOURCES/httpd-2.0.51.tar.gz
> >
> > sorry I don't want to wait more than 10 minutes to send that mail, but=20
> > again seeing the files apperaing very slowly on the tty it seems not=20
> > to be the solution :-( .

The following script may help you understand why things are slower in
the case of "async" on an untar. It basically just creates a bunch of
files: in the first test it does not sync the directory to disk after
each file creation, in the second case it does. The test does no
reads/writes to the file.

Run it on the server and you will see  a clear difference in time
between test1 and test2. Run it on the client, and there should be
little difference between test1 and test2 (but there will be a heavy
dependency on the "async" vs "sync" export flag on the server).

NFSv3 mandates that all directory-related operations should behave as in
test 2. Only writes to ordinary files may be cached by the server, and
when the client sends a COMMIT request, the server should do an fsync()
on that file.

Cheers,
  Trond
--=20
Trond Myklebust <trond.myklebust@fys.uio.no>

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#!/bin/bash
#
test1()
{
	(
	rm -rf test_dir1
	mkdir test_dir1
	cd test_dir1
	i=0
	while [ $i -lt 1000 ]
	do
		echo -n "" >file$i
		i=$(($i + 1))
	done
	)
}

test2()
{
	(
	rm -rf test_dir2
	mkdir test_dir2
	cd test_dir2
	i=0
	while [ $i -lt 1000 ]
	do
		echo -n "" >file$i
		sync
		i=$(($i + 1))
	done
	)
}

sync
echo "Test without directory sync after file creation"
time test1
sync
echo "Test2 with directory sync after file creation"
time test2

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