On Jul 20, 2009 19:04 -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.
>
> (Sorry for the whitespace damage.)
>
> -VAL
>
> 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.
I would make this a bit more clear:
This option sets the default journal mode for ext3 filesystems
which do not explicitly specify it in /etc/fstab or at mount
time. It is always possible to set the journal mode for each
filesystem independently with "data=writeback", "data=ordered",
or "data=journal" mount options.
> The journal mode options for ext3 have different tradeoffs
> between when data is guaranteed to be on disk and
> performance. Many applications assume "data=ordered"
> semantics and may lose, destroy, or reveal other user's data
> in other journal modes. However, "data=ordered" mode can
> also result in major performance problems, including long
> delays before an fsync() call returns. For details, see:
I think the "... lose, destroy, ..." part is confusing, as it mentions
"data=ordered" first and it isn't until the end of the sentence that
it is clear that "lose, destroy, ..." does not apply to data=ordered.
Also "data=journal" also does not apply in this case, only "data=writeback"
so we may as well call that out explicitly.
... Many applications do not explicitly sync data and assume
"data=ordered" mode. Saying 'N' here will use "data=writeback"
as the default for all ext3 filesystems, and may result in
files with no data, or garbage data from deleted files,
which is a security risk on a multi-user system. However, ...
> XXX some document
>
> Use "data=ordered" mode unless you know it is causing a
> performance problem for your workload.
>
> If you are unsure, say 'Y'.
Cheers, Andreas
--
Andreas Dilger
Sr. Staff Engineer, Lustre Group
Sun Microsystems of Canada, Inc.
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