[Linux-ha-dev] Hi list!!

[Frank Peter Rival USG]

Sean Reifschneider wrote:

> On Wed, Oct 20, 1999 at 05:46:10PM +0100, Stephen C. Tweedie wrote:
> >Yes --- or rather, journaling is one method by which we can make a
> >filesystem transactional.
>
> As I understand it, the journaling in ext3 (which is a fantastic
> design, BTW), only handles journaling of file-system meta-data,
> not of actual file data.  This is a common misconception I've run
> into is that it handles the file data as well.

Bzzt.  As a matter of fact, all it does right now is journal both data and
metadata.  Stephen mentioned that we could try turning off data logging (thereby
improving vastly the performance) but that it certainly hadn't been tested.

>
> The problem is that in the event of a crash, there's little a file-system
> can do to prevent the crashed applications data from being left in an
> unknown state.
>

Yup.  Even with data logging, who is to say that the last write you did to a file
actually leaves your file in a usable state, for example?  I believe that's why
Alan is so high on RAID-1+NBD - the data is written to all nodes simultaneously,
so unless your entire cluster crashes, at least someone has the right data.
Again, not super-performing (and sct has mentioned that there are tweaks we can
use) but pretty doggone stable.

 - Pete