linux-kernel - Re: io-scheduler tuning for better read/write ratio

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Message-Id: <200906241057.41227.a1426z@gawab.com>
Date:	Wed, 24 Jun 2009 10:57:41 +0300
From:	Al Boldi <a1426z@...ab.com>
To:	Ralf Gross <Ralf-Lists@...fgross.de>
Cc:	linux-kernel@...r.kernel.org, fengguang.wu@...el.com
Subject: Re: io-scheduler tuning for better read/write ratio

Ralf Gross wrote:
> The main problem is with bacula. It reads/writes from/to two
> spoolfiles on the same device.
>
> I get the same behavior with 2 dd processes, one reading from disk, one
> writing to it.
>
> Here's the output from dstat (5 sec intervall).
>
> --dsk/md1--
> _read _writ
>   26M   95M
>   31M   96M
>   20M   85M
>   31M  108M
>   28M   89M
>   24M   95M
>   26M   79M
>   32M  115M
>   50M   74M
>  129M   15k
>  147M 1638B
>  147M    0
>  147M    0
>  113M    0
>
>
> At the end I stopped the dd process that is writing to the device, so you
> can see that the md device is capable of reading with >120 MB/s.
>
> I did this with these two commands.
>
> dd if=/dev/zero of=test bs=1MB
> dd if=/dev/md1 of=/dev/null bs=1M

Try changing /proc/sys/vm/dirty_ratio = 1


Thanks!

--
Al

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