From: John Robinson <john.robinson@anonymous.org.uk>
To: Justin Piszcz <jpiszcz@lucidpixels.com>
Cc: linux-raid@vger.kernel.org, xfs@oss.sgi.com
Subject: Re: Linux RAID & XFS Question - Multiple levels of concurrency = faster I/O on md/RAID 5?
Date: Sat, 01 Nov 2008 12:14:44 +0000 [thread overview]
Message-ID: <490C4834.3050404@anonymous.org.uk> (raw)
In-Reply-To: <alpine.DEB.1.10.0811010758240.1053@p34.internal.lan>
On 01/11/2008 12:00, Justin Piszcz wrote:
> On Sat, 1 Nov 2008, John Robinson wrote:
>> On 01/11/2008 08:29, Justin Piszcz wrote:
>> [...]
>>> Why is running 3 jobs con-currently that take care of two parts each
>>> more than
>>> twice as fast than running one job for six parts?
>>
>> Because you have multiple CPUs?
>
> So 1/4 of a quad core q6600 cannot achieve higher rates of I/O due to the
> parity operations being that costly?
>
> Is the only way to increase the single-threaded speed to increase the
> maximum
> CPU core speed/get a faster CPU, and/or theoretically a multi-threaded
> md-raid
> could maximize throughput?
Actually I was thinking that your test job - I think you said it used
tar - is single-threaded and CPU-bound on one core, and doesn't saturate
the MD subsystem. Your jobs are 75% user time to 25% system time, and
the user time is not parellelisable until you do it yourself by
splitting the work up.
Cheers,
John.
next prev parent reply other threads:[~2008-11-01 12:14 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2008-11-01 8:29 Linux RAID & XFS Question - Multiple levels of concurrency = faster I/O on md/RAID 5? Justin Piszcz
2008-11-01 10:55 ` John Robinson
2008-11-01 12:00 ` Justin Piszcz
2008-11-01 12:14 ` John Robinson [this message]
2008-11-02 22:03 ` Dave Chinner
2008-11-02 22:21 ` Dan Williams
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