Re: 2.6.30

["Todd A. Jacobs" <nospam@codegnome.org>]

On Wed, Jun 17, 2009 at 07:23:27PM +0300, David Baron wrote:

> 1. Ext3 fs now default to writeback data mode instead of ordered-data.
> I does seem quicker. Question is whether this mode is safe? Should I
> tune2fs back? Should I use extents along with the writeback data mode?

Ordered-data is safer than writeback, as writeback doesn't make any
guarantees about data at all. From the mount man page:

    journal
	 All data is committed into the journal prior to being written
	 into the main file system.

    ordered
	 This is the default mode.  All data is forced directly out to
	 the main file system prior to its metadata  being  committed
	 to  the journal.

    writeback
	 Data ordering is not preserved - data may be written into the
	 main file system after its metadata has been committed to the
	 journal. This is rumoured to be the highest-throughput option.
	 It guarantees internal file system integrity, however it can
	 allow  old  data to appear in files after a crash and journal
	 recovery.

You should only use writeback on partitions where data integrity isn't
critical, IMHO. Writeback essentially only guarantees that you won't
have to wait forever for fsck, not that your data is safe or committed
atomically.

As for extents, they aren't supported in ext3 anyway. You'd need to
reformat (not upgrade an existing partition) to ext4 to make use of
them.

-- 
"Oh, look: rocks!"
	-- Doctor Who, "Destiny of the Daleks"