ext3: Update Kconfig description of EXT3_DEFAULTS_TO_ORDERED

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.

Cc: linux-ext4@vger.kernel.org
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Signed-off-by: Jan Kara <jack@suse.cz>

1 files changed, 17 insertions, 15 deletions

diff --git a/fs/ext3/Kconfig b/fs/ext3/Kconfig
index fb3c1a21b13..522b15498f4 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"