From: Trond Myklebust <trond.myklebust@fys.uio.no>
Subject: Re: can anyone explain this state?
Date: Wed, 17 Aug 2005 08:39:52 -0400
Message-ID: <1124282392.23245.26.camel@lade.trondhjem.org>
References: <bc57270905081704131c4b23d4@mail.gmail.com>
	 <1124280174.23245.4.camel@lade.trondhjem.org> <43032CF2.3070908@redhat.com>
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Content-Type: text/plain
Cc: Michael <mikore.li@gmail.com>, nfs@lists.sourceforge.net
To: Peter Staubach <staubach@redhat.com>
In-Reply-To: <43032CF2.3070908@redhat.com>
Sender: nfs-admin@lists.sourceforge.net
Errors-To: nfs-admin@lists.sourceforge.net

on den 17.08.2005 Klokka 08:26 (-0400) skreiv Peter Staubach:
> Trond Myklebust wrote:
> 
> >on den 17.08.2005 Klokka 19:13 (+0800) skreiv Michael:
> >  
> >
> >>Hi, 
> >>
> >>These day, I observed a strange thing when I copy a 100MB file from
> >>nfs server, both client and server is running redhat 9.0 with kernel
> >>2.4.20-8:
> >>
> >>$ sudo mount -o
> >>rw,bg,vers=3,tcp,timeo=600,rsize=1024,wsize=1024,hard,intr,ac
> >>server1:/home/test filetest
> >>$ time cp ./filetest/new100m /tmp/o100m
> >>
> >>real    1m6.575s
> >>user    0m0.040s
> >>sys     0m1.430s
> >>$ time cp ./filetest/new100m /tmp/o100m
> >>
> >>real    0m4.964s     =================> it is so different comparing
> >>with above time!!
> >>user    0m0.030s
> >>sys     0m0.570s
> >>    
> >>
> >
> >This is done using synchronous writes. Each write will wait for the
> >server to commit it to disk.
> >
> >  
> >
> >>$ sudo umount filetest
> >>$ sudo mount -o
> >>rw,bg,vers=3,tcp,timeo=600,rsize=102400,wsize=102400,hard,intr,ac
> >>server1:/home/test filetest
> >>$ time cp ./filetest/new100m /tmp/o100m
> >>
> >>real    0m9.075s
> >>user    0m0.020s
> >>sys     0m0.470s
> >>$ time cp ./filetest/new100m /tmp/o100m
> >>
> >>real    0m7.501s    ==================>only different in 2 seconds!
> >>why not less than 4.9 seconds?
> >>user    0m0.000s
> >>sys     0m0.520s
> >>    
> >>
> >
> >This is done using asynchronous writes. Much faster, and no need (on
> >NFSv3) to wait for the disk before sending the next request.
> >
> >The reason is that on 2.4 kernels (and early 2.6 kernels) we could only
> >do synchronous writes when you set wsize < PAGE_SIZE.
> >
> 
> Maybe I am misreading the commands being run, but they look like they would
> generate all NFS READ traffic.  It appears to be copying from an NFS mounted
> file system to /tmp, a local file system.

Oops. errno=ENOCOFFEE... You are quite right.

Yep. That would indeed put the differences down to caching.

Cheers,
  Trond


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