On Mon, Dec 09, 2002 at 10:20:21PM +0100, Manuel Bouyer wrote:

 > This is easy to do. Unfortunably, I don't think the filesystems will pass
 > us this info ...

Right, the file system needs to insert explicit barriers.  For SCSI
disks, this would issue a "SYNCHRONIZE CACHE" command.

I've discussed the need for this with Kirk McKusick on at least 2
occasions, but it's been ... extraordinarily hard to convince him
that it's needed.  His response is always "well, use tagged queueing
then", but what he keeps missing is that the data might not be on
the media *even if the disk says the command has completed*.

Sigh.  This would have been a perfect infrastructure improvement for
his "UFS2", as well.

-- 
        -- Jason R. Thorpe <thorpej@wasabisystems.com>