From: Stan Hoeppner <stan@hardwarefreak.com>
To: Nikolaus Jeremic <jeremic@informatik.uni-rostock.de>,
linux-raid@vger.kernel.org
Subject: Re: RAID 6 reads all remaining chunks in a stripe when a single chunk is rewritten
Date: Tue, 17 Dec 2013 07:02:29 -0600 [thread overview]
Message-ID: <52B04B65.7070603@hardwarefreak.com> (raw)
In-Reply-To: <52B02A08.4090007@informatik.uni-rostock.de>
On 12/17/2013 4:40 AM, Nikolaus Jeremic wrote:
> Hi,
>
> I've did some Linux MD RAID 5 and 6 random write performance tests with
> fio 2.1.2 (Flexible I/O tester) under Linux 3.12.4. However, the results
> for RAID 6 show that writes to a single chunk in a stripe (chunk size is
> 64 KB) result in more than 3 reads in case of more than 6 drives (tested
> with 7, 8, and 9 drives) in the array (see fio statistics below). It
> seems like that in the event of updating one data chunk in a stripe, all
> of the remaining data chunks are read.
>
> By the way, in case of RAID 5 and 5 or more drives, the remaining chunks
> seem not to be read when updating a single chunk in a stripe.
>
> Here is the fio job description:
<snip>
It would be easier and more deterministic if you'd simply use dd to
write one full stripe, then seek to one chunk within that stripe and
write one page.
--
Stan
next prev parent reply other threads:[~2013-12-17 13:02 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-12-17 10:40 RAID 6 reads all remaining chunks in a stripe when a single chunk is rewritten Nikolaus Jeremic
2013-12-17 13:02 ` Stan Hoeppner [this message]
2013-12-17 13:39 ` Phil Turmel
2013-12-17 13:51 ` Peter Grandi
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