From: Goswin von Brederlow <goswin-v-b@web.de>
To: Matthias Dahl <ml_linux_raid@mortal-soul.de>
Cc: Goswin von Brederlow <goswin-v-b@web.de>, linux-raid@vger.kernel.org
Subject: Re: partitioned raid 5 and proper partition alignment
Date: Sun, 09 Aug 2009 00:21:35 +0200 [thread overview]
Message-ID: <87ws5egd5c.fsf@frosties.localdomain> (raw)
In-Reply-To: <200908081309.59049.ml_linux_raid@mortal-soul.de> (Matthias Dahl's message of "Sat, 8 Aug 2009 13:09:59 +0200")
Matthias Dahl <ml_linux_raid@mortal-soul.de> writes:
> Hi.
>
> On Saturday 08 August 2009 09:56:59 you wrote:
>
>> But each stripe only holds 128k of data. You have to align to that.
>
> I beg to differ. There are two data chunks and one parity chunk, thus a whole
> stripe is 192k long if you've a 64k chunk size. If you align to 128k and you
> put e.g. ext4 on it with the correct fs stride and stripe-width settings,
> you'll probably end up with worse performance since you start in the middle of
> a stripe even though properly aligned to a chunk boundary. Or am I totally on
> the wrong track here...?!
Yes you are. The filesystem will never ever see the parity block of a
stripe. It only ever sees the 128k data. Writing 128k data will write
a full stripe of 192k to disk.
MfG
Goswin
prev parent reply other threads:[~2009-08-08 22:21 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-08-08 6:12 partitioned raid 5 and proper partition alignment Matthias Dahl
2009-08-08 7:56 ` Goswin von Brederlow
2009-08-08 11:09 ` Matthias Dahl
2009-08-08 22:21 ` Goswin von Brederlow [this message]
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