Re: libata in 2.4.24?

From: Jeff Garzik
Date: Tue Dec 02 2003 - 13:08:31 EST

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?

Yes, it does. But it depends on whether or not the host controller
supports 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.

If true, this is an IDE driver bug... assuming the drive itself
doesn't lie about FLUSH CACHE results (a few do).

> 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.

If the drive lies, there isn't a darned thing we can do about it...

> Do the new SATA drives and controllers provide a solution to this?

If the drive lies, there isn't a darned thing the controller can do
about it, either ;-)


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