linux-ext4 - Why does journal mode outperforms all other modes when reading and writing data at the same time?

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Date:	Tue, 28 May 2013 22:39:18 +0800
From:	jingguo yao <yaojingguo@...il.com>
To:	linux-ext4@...r.kernel.org
Subject: Why does journal mode outperforms all other modes when reading and
 writing data at the same time?

Documentation/filesystems/ext4.txt has the following sentence:

  This mode is the slowest except when data needs to be read from and
  written to disk at the same time where it outperforms all others
  modes.

And the following link talks about it in more details. Can anybody give
the reason?

http://www.ibm.com/developerworks/library/l-fs8/index.html#4

--
Jingguo
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