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

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Message-ID: <x49fxdsl46y.fsf@segfault.boston.devel.redhat.com>
Date:	Mon, 22 Jun 2009 10:43:17 -0400
From:	Jeff Moyer <jmoyer@...hat.com>
To:	Ralf Gross <rg@...-softwaretechnik.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: io-scheduler tuning for better read/write ratio

Jeff Moyer <jmoyer@...hat.com> writes:

> Ralf Gross <rg@...-softwaretechnik.com> writes:
>
>> Casey Dahlin schrieb:
>>> On 06/16/2009 02:40 PM, Ralf Gross wrote:
>>> > David Newall schrieb:
>>> >> Ralf Gross wrote:
>>> >>> write throughput is much higher than the read throughput (40 MB/s
>>> >>> read, 90 MB/s write).
>>> > 
>>> > Hm, but I get higher read throughput (160-200 MB/s) if I don't write
>>> > to the device at the same time.
>>> > 
>>> > Ralf
>>> 
>>> How specifically are you testing? It could depend a lot on the
>>> particular access patterns you're using to test.
>>
>> I did the basic tests with tiobench. The real test is a test backup
>> (bacula) with 2 jobs that create 2 30 GB spool files on that device.
>> The jobs partially write to the device in parallel. Depending which
>> spool file reaches the 30 GB first, one starts reading from that file
>> and writing to tape, while to other is still spooling.
>
> We are missing a lot of details, here.  I guess the first thing I'd try
> would be bumping up the max_readahead_kb parameter, since I'm guessing
> that your backup application isn't driving very deep queue depths.  If
> that doesn't work, then please provide exact invocations of tiobench
> that reprduce the problem or some blktrace output for your real test.

Any news, Ralf?

Cheers,
Jeff
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