linux-ext4 - [Bug 71641] New: Unreasonable performance degradation in ext4 with full data journaling

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Date:	Fri, 07 Mar 2014 11:39:40 +0000
From:	bugzilla-daemon@...zilla.kernel.org
To:	linux-ext4@...r.kernel.org
Subject: [Bug 71641] New: Unreasonable performance degradation in ext4 with
 full data journaling

https://bugzilla.kernel.org/show_bug.cgi?id=71641

            Bug ID: 71641
           Summary: Unreasonable performance degradation in ext4 with full
                    data journaling
           Product: File System
           Version: 2.5
    Kernel Version: 3.4.6
          Hardware: x86-64
                OS: Linux
              Tree: Mainline
            Status: NEW
          Severity: normal
          Priority: P1
         Component: ext4
          Assignee: fs_ext4@...nel-bugs.osdl.org
          Reporter: fredchang.tc@...il.com
        Regression: No

JFS provides three modes, journal, ordered and writeback.
The first mode is denoted as ‘journal mode’in the following context.
In the journal mode, data should be written twice, one for the journal area and
the other for the client file system. If the journal area and the client file
system are both located in the disk, it has at least 50% performance
degradation compared to ordered mode.
But what if we put the journal area in a ramdisk?
I did the following tests. It shows the ext4 with full data journaling has
unreasonable performance degradation even the journal area is located in the
ramdisk.

Test environment--  
CPU: Intel(R) Xeon(R) CPU E3-1225 v3 @ 3.20GHz
RAM:8GB
Filesystem:Ext4
Linux version:3.4.6
RAID are composed of 6 x 1TB HD
Command: time dd if=/dev/zero of= Write_File bs=1M count=51200

Volume_type ordered_mode Journal_mode degradation
Single_disk    173MB/s    144MB/s    17%
RAID0        937MB/s    375MB/s    60%
RAID5       732MB/s    132MB/s    82%

Does anyone know where the bottleneck may be?

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