linux-kernel - Re: Understanding I/O behaviour

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Date:	Fri, 6 Jul 2007 03:18:40 -0700 (PDT)
From:	Martin Knoblauch <spamtrap@...bisoft.de>
To:	linux-kernel@...r.kernel.org
Subject: Re: Understanding I/O behaviour

>>    b) any ideas how to optimize the settings of the /proc/sys/vm/
>>    parameters? The documentation is a bit thin here.
>>
>>
>I cant offer any advice there, but is raid-5 really the best choice
>for your needs? I would not choose raid-5 for a system that is
>regularly performing lots of large writes at the same time, dont
>forget that each write can require several reads to recalculate the
>partity.
>
>Does the raid card have much cache ram?
>

 192 MB, split 50/50 to read write.

>If you can afford to loose some space raid-10 would probably perform
>better.

 RAID5 most likely is not the best solution and I would not use it if
the described use-case was happening all the time. It happens a few
times a day and then things go down when all memory is filled with
page-cache.

 And the same also happens when copying large amountd of data from one
NFS mounted FS to another NFS mounted FS. No disk involved there.
Memory fills with page-cache until it reaches a ceeling and then for
some time responsiveness is really really bad.

 I am just now playing with the dirty_* stuff. Maybe it helps.

Cheers
Martin

------------------------------------------------------
Martin Knoblauch
email: k n o b i AT knobisoft DOT de
www:   http://www.knobisoft.de
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