Re: libata in 2.4.24?

[Jens Axboe]

On Tue, Dec 02 2003, Mike Fedyk wrote:
> On Tue, Dec 02, 2003 at 11:31:45AM -0500, Greg Stark wrote:
> > 
> > Mike Fedyk <mfedyk@xxxxxxxxxxxxx> writes:
> > 
> > > > Libata, uses the scsi system instead of the existing ide layer because many
> > > > new sata controllers are using an interface that is very similair to scsi
> > > > (much like atapi).
> > 
> > Now I have a different question. Does the scsi-like SATA interface include tcq?
> > 
> > Because one of the long-standing issues with IDE drives and Postgres is the
> > fact that even after issuing an fsync the data may be sitting in the drive's
> > buffer. This doesn't happen with SCSI because the drives aren't forced to lie
> > about the data being on disk in order to handle subsequent requests. Turning
> > off write-caching on IDE drives absolutely destroys performance.
> 
> There are PATA drives that do TCQ too, but you have to look for that feature
> specifically.  IDE TCQ is in 2.6, but is still experemental.  I think Jens
> Axboe was the one working on it IIRC.  He would have more details.

Yes that was me. PATA TCQ is currently disabled in the 2.6 kernel
configs, and it will most likely just go away sometime soonish. It's not
a very useful feature, PATA TCQ is pretty broken. I knew this from the
beginning, but thought that it would be fun to try it in real life. It's
just not worth it, though.

SATA host queueing support will be useful.

-- 
Jens Axboe

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