linux-ext4 - Re: [PATCH, RFC] ext3: Update Kconfig description of EXT3_DEFAULTS_TO

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Message-ID: <4A80894A.7050506@redhat.com>
Date:	Mon, 10 Aug 2009 16:55:38 -0400
From:	Ric Wheeler <rwheeler@...hat.com>
To:	"Theodore Ts'o" <tytso@....edu>
CC:	Jan Kara <jack@...e.cz>,
	Linux Kernel Developers List <linux-kernel@...r.kernel.org>,
	linux-ext4@...r.kernel.org
Subject: Re: [PATCH, RFC] ext3: Update Kconfig description of EXT3_DEFAULTS_TO_ORDERED

On 08/10/2009 04:03 PM, Theodore Ts'o wrote:
> The old description for this configuration option was perhaps not
> completely balanced in terms of describing the tradeoffs of using a
> default of data=writeback vs. data=ordered.  Despite the fact that old
> description very strongly recomended disabling this feature, all of
> the major distributions have elected to preserve the existing 'legacy'
> default, which is a strong hint that it perhaps wasn't telling the
> whole story.
>
> This revised description has been vetted by a number of ext3
> developers as being better at informing the user about the tradeoffs
> of enabling or disabling this configuration feature.
>
> Signed-off-by: "Theodore Ts'o"<tytso@....edu>
> Cc: linux-ext4@...r.kernel.org
>    

Thanks Ted - this is much more informative and will allow for a more 
informed trade off to be made,

Ric

> ---
>   fs/ext3/Kconfig |   32 +++++++++++++++++---------------
>   1 files changed, 17 insertions(+), 15 deletions(-)
>
> diff --git a/fs/ext3/Kconfig b/fs/ext3/Kconfig
> index fb3c1a2..522b154 100644
> --- a/fs/ext3/Kconfig
> +++ b/fs/ext3/Kconfig
> @@ -29,23 +29,25 @@ config EXT3_FS
>   	  module will be called ext3.
>
>   config EXT3_DEFAULTS_TO_ORDERED
> -	bool "Default to 'data=ordered' in ext3 (legacy option)"
> +	bool "Default to 'data=ordered' in ext3"
>   	depends on EXT3_FS
>   	help
> -	  If a filesystem does not explicitly specify a data ordering
> -	  mode, and the journal capability allowed it, ext3 used to
> -	  historically default to 'data=ordered'.
> -
> -	  That was a rather unfortunate choice, because it leads to all
> -	  kinds of latency problems, and the 'data=writeback' mode is more
> -	  appropriate these days.
> -
> -	  You should probably always answer 'n' here, and if you really
> -	  want to use 'data=ordered' mode, set it in the filesystem itself
> -	  with 'tune2fs -o journal_data_ordered'.
> -
> -	  But if you really want to enable the legacy default, you can do
> -	  so by answering 'y' to this question.
> +	  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_mode_tradeoffs
> +
> +	  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'.
>
>   config EXT3_FS_XATTR
>   	bool "Ext3 extended attributes"
>    

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