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To: Julian Elischer <julian@elischer.org>
From: "Poul-Henning Kamp" <phk@phk.freebsd.dk>
In-Reply-To: Your message of "Sat, 30 Jul 2005 03:29:27 PDT."
	<42EB5687.2070400@elischer.org> 
Date: Sat, 30 Jul 2005 12:33:55 +0200
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Cc: FreeBSD Current <freebsd-current@freebsd.org>
Subject: Re: Apparent strange disk behaviour in 6.0 
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In message <42EB5687.2070400@elischer.org>, Julian Elischer writes:
>Poul-Henning Kamp wrote:
>> In message <42E88135.30603@elischer.org>, Julian Elischer writes:
>> 
>> Please use gstat and look at the service times instead of the 
>> busy percentage.
>
>The snapshot below is typical when doing tar from one drive to another..
>(tar c -C /disk1 f- .|tar x -C /disk2 -f - )
>
>dT: 1.052  flag_I 1000000us  sizeof 240  i -1
>  L(q)  ops/s    r/s   kBps   ms/r    w/s   kBps   ms/w    d/s   kBps   ms/d %busy Name
>     0    405    405   1057    0.2      0      0    0.0      0      0    0.0 9.8  | ad0
>     0    405    405   1057    0.3      0      0    0.0      0      0    0.0 11.0 | ad0s2
>     0    866      3     46    0.4    863   8459    0.7      0      0    0.0 63.8 | da0
>    25    866      3     46    0.5    863   8459    0.8      0      0    0.0 66.1 | da0s1
>     0    405    405   1057    0.3      0      0    0.0      0      0    0.0 12.1 | ad0s2f
>   195    866      3     46    0.5    863   8459    0.8      0      0    0.0 68.1 | da0s1d
>
>even though the process should be disk limitted neither of the disks is anywhere
>near 100%.

This looks like an awful lot of small files since you write 8 times as much data
as you read ?

Since the write service time (ms/w) is low, I pressume you have
some hefty disk hardware (with cache ?)

Presumably you're using softupdates ?

I wouldn't be surprised if you were limited by system time rather than disk in
this scenario ?

-- 
Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
phk@FreeBSD.ORG         | TCP/IP since RFC 956
FreeBSD committer       | BSD since 4.3-tahoe    
Never attribute to malice what can adequately be explained by incompetence.