Re: [linux-lvm] EXT2 to EXT3 LVM volume on Redhat

[Stephen Tweedie <sct@redhat.com>]

Hi,

On Thu, Jun 06, 2002 at 08:31:30AM +1200, Steve Wray <steve.wray@paradise.net.nz> wrote:

> /dev/system/home /home ext3 data=journal 1 2
> 
> Its the bomb. I have a hell of a lot of dynamic data
> in that /home so in event of a crash there was a big
> chance of corruption. Not Any More!!!!!
> 8-)

I'm not quite sure why people think that data=journal is any "safer"
than the default data=ordered mode.  In fact, data=ordered could well
be safer simply because the default mode is probably in use on more
systems, and so is better tested.  :-)

data=journal writes the data to the journal as well as the metadata,
but *both* ordered and data modes flush data to disk carefully as part
of their transaction commit.  If you create new files with the default
of data=ordered, there is still an absolute guarantee that a
transaction commit will show all the data safe on disk, and you will
never see stale data blocks show up on disk after a crash.

Only the looser "data=writeback" mode of ext3 relaxes this guarantee
and makes data writes independent of metadata writes, as they are for
most other filesystems.

Cheers,
 Stephen