Re: 2.6.30



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"


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