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Date: Mon, 12 Nov 2001 13:43:37 -0800
From: Andrew Morton <akpm@zip.com.au>
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To: Steve Lord <lord@sgi.com>
CC: Ben Israel <ben@genesis-one.com>, linux-kernel@vger.kernel.org
Subject: Re: File System Performance
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Steve Lord wrote:
> 
> ...
> 
> I tried an experiment which puzzled me somwhat:
> 
> >  mount /xfs
> >  cd /xfs/lord/xfs-linux
> >  time tar cf /dev/null linux
> 
> real    0m7.743s
> user    0m0.510s
> sys     0m1.380s
> 
> > hdparm -t /dev/sda5
> 
> /dev/sda5:
>  Timing buffered disk reads:  64 MB in  3.76 seconds = 17.02 MB/sec
> 
> > du -sk linux
> 173028  linux
> 
> The tar got ~21 Mbytes/sec.
>

It's tar.  It cheats.  It somehow detects that the
output is /dev/null, and so it doesn't read the input files.
I think.

akpm-1:/opt> l
total 562884
-rw-r--r--    1 akpm     akpm     575785370 Apr  8  2001 backup

akpm-1:/opt> time tar cf /dev/null backup
tar cf /dev/null backup  0.02s user 0.00s system 4% cpu 0.422 total

That's 570 megs in 0.4 seconds.  Impressive.

So I just use
	time (find dir -type f | xargs cat > /dev/null)

> In our cvs tree cmd/xfsprogs/tests/src/fsstress.c

OK, thanks.

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