[linux-lvm] EXT2 to EXT3 LVM volume on Redhat
Stephen Tweedie
sct at redhat.com
Mon Jun 24 08:41:01 UTC 2002
Hi,
On Thu, Jun 06, 2002 at 08:31:30AM +1200, Steve Wray <steve.wray at 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
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