On Mon, Dec 09, 2002 at 02:31:38PM -0800, Jason R Thorpe wrote:
> On Mon, Dec 09, 2002 at 11:27:25PM +0100, Manuel Bouyer wrote:
> 
>  > This would be expensive. I think you just need to know *some* commands are
>  > written to disk, but not all of them. So it's probably better to have this
>  > information per command, instead of barriers that would flush the whole cache.
> 
> Except, when you write an update to an inode that changes the file size
> indication, you bloody well want to make sure that the data blocks you
> just wrote are on the platter.
> 
>  > Hum, I think with tagged queuing, the command won't complete before
>  > data is on the media.
> 
> Are you *sure*?  I'm not certain that this is actually a requirement,
> and I have some emperical data which suggests that its not the case.  I.e.
> I have disks where tagged queueing is being used, and write speed goes WAY
> up when the write-cache is enabled.

If you explicitely enable write-back maybe it's not (it would make sense).
I'll check it when I'm back home.

--
Manuel Bouyer, LIP6, Universite Paris VI.           Manuel.Bouyer@lip6.fr
     {Net,Free}BSD: 23 ans d'experience feront toujours la difference
--