linux-ext4 - Re: ext3 default journal mode

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Date:	Thu, 23 Jul 2009 09:14:29 -0400
From:	Ric Wheeler <rwheeler@...hat.com>
To:	Valerie Aurora <vaurora@...hat.com>
CC:	Theodore Tso <tytso@....edu>, Ric Wheeler <rwheeler@...hat.com>,
	"linux-ext4@...r.kernel.org" <linux-ext4@...r.kernel.org>,
	"Stephen C. Tweedie" <sct@...hat.com>,
	Eric Sandeen <esandeen@...hat.com>,
	Andreas Dilger <adilger@....com>,
	Chris Mason <chris.mason@...cle.com>,
	Josef Bacik <jbacik@...hat.com>, Mingming Cao <cmm@...ibm.com>
Subject: Re: ext3 default journal mode

On 07/21/2009 01:44 PM, Valerie Aurora wrote:
> On Mon, Jul 20, 2009 at 10:00:50PM -0400, Theodore Tso wrote:
>    
>> On Mon, Jul 20, 2009 at 07:04:03PM -0400, Valerie Aurora wrote:
>>      
>>> I think it's extremely accurate and detailed, but too long - people's
>>> brains turn off after about the 15th line or so.  Here's an attempt to
>>> distill your description down and refer out to another document (which
>>> one?) for people who want to learn more.
>>>        
>> Fair enough;  I've created an external document here:
>>
>> http://ext4.wiki.kernel.org/index.php/Ext3_Data%3DOrdered_vs_Data%3DWriteback_mode
>>
>> Comments?
>>      
>
> Nice!
>
>    
>>>   config EXT3_DEFAULTS_TO_ORDERED
>>>   	bool "Default to 'data=ordered' in ext3"
>>>   	depends on EXT3_FS
>>>   	help
>>>
>>>            If the mount options for an ext3 filesystem do not
>>>            include a journal mode, mount it in "data=ordered" mode.
>>>        
>> Let me give a try at this:
>>
>>             The journal mode options for ext3 have different tradeoffs
>>             between when data is guaranteed to be on disk and
>>             performance.  The use of "data=writeback" can cause
>>             unwritten data to appear in files after an system crash or
>>             power failure, which can be a security issue.  However,
>>             "data=ordered" mode can also result in major performance
>>             problems, including seconds-long delays before an fsync()
>>             call returns.  For details, see:
>>
>> 	   http://ext4.wiki.kernel.org/index.php/Ext3_Data%3DOrdered_vs_Data%3DWriteback_mode
>>
>>            If you have been historically happy with ext3's performance,
>>            data=ordered mode will be a safe choice and you should
>>            answer "y" here.  If you understand the reliability and data
>>            privacy issues of data=writeback and are willing to make
>>            that trade off, answer "n".
>>      
>
> This is great.  Ship it!
>
> -VAL
>    

I certainly agree - this is a vast improvement over what we have today, 
thanks!

Ric

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