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

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Message-ID: <20090622163113.GD12483@p15145560.pureserver.info>
Date:	Mon, 22 Jun 2009 18:31:13 +0200
From:	Ralf Gross <rg@...-Softwaretechnik.com>
To:	linux-kernel@...r.kernel.org
Subject: Re: io-scheduler tuning for better read/write ratio

Jeff Moyer schrieb:
> 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?

sorry for the delay. atm there are large backups running and using the
raid device for spooling. So I can't do any tests.

Re. read ahead: I tested different settings from 8Kb to 65Kb, this
didn't help.

I'll do some more tests when the backups are done (3-4 more days).

Thanks, Ralf

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