Re: XFS and write barriers.

[Neil Brown <neilb@xxxxxxx>]

On Sunday March 25, dgc@xxxxxxx wrote:
> On Fri, Mar 23, 2007 at 07:00:46PM +1100, Neil Brown wrote:
> > 
> > Why no barriers on an external log device??? Not important, just
> > curious.
> 
> because we need to synchronize across 2 devices, not one, so issuing
> barriers on an external log device does nothing to order the metadata
> written to the other device...

Right, of course.  Just like over a raid0.

So you must have code to wait for all writes to the main device before
writing the commit block on the journal.   How hard is it to fall-back
to that if the barrier fails?

NeilBrown