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.

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