linux-kernel - Re: PATA-disk named sda

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Message-Id: <200707062009.08635.bzolnier@gmail.com>
Date:	Fri, 6 Jul 2007 20:09:08 +0200
From:	Bartlomiej Zolnierkiewicz <bzolnier@...il.com>
To:	Robert Hancock <hancockr@...w.ca>
Cc:	Christoph Pleger <Christoph.Pleger@...uni-dortmund.de>,
	linux-kernel@...r.kernel.org
Subject: Re: PATA-disk named sda


Hi,

On Friday 06 July 2007, Robert Hancock wrote:
> Christoph Pleger wrote:
> > Hello,
> > 
> >>> In the newest Ubuntu Release, my PATA-disk is called sda instead of
> >>> hda. Is that a general feature in newer kernel versions or is it a
> >>> special feature in Ubuntu?
> >> General. SATA and now PATA drives map onto the /dev/sd range as do
> >> SCSI, USB etc
> > 
> > It seems to be not that simple, at least not if both the old IDE
> > interface and the new libata interface are enabled as modules: In my
> > Ubuntu system, I created two kernel packages (from the same kernel
> > source and with the same configuration) and installed them. Afterwards,
> > I re-created the initial ramdisks, one with the Ubuntu feisty utilities
> > and one with Debian etch utilities. So, I had the same kernel with
> > different ramdisks. With the Ubuntu ramdisk, my harddrive was named sda,
> > but with the Debian ramdisk, it was named hda.
> > 
> > So, the name of the drive can depend on something which happens in the
> > ramdisk environment. Does anybody know what that is? And is there a
> > kernel command line parameter which restores the old behaviour?
> > 
> > And what about hdparm (setting 32bit I/O and multi-sector mode)? Suren
> > wrote that 32bit I/O makes no sense when using DMA. Maybe that's right,
> > but it does not correspond with my experiences. At least, I have the
> > "feeling" that my IDE disks work much faster since I enabled 32bit
> > support (DMA already was on before).
> 
> No, it has absolutely no effect in DMA mode.
> 
> Currently the DMA, multi-sector mode, etc. are not controllable with 
> hdparm with libata. libata is designed to use the fastest settings 
> possible by default. In a lot of cases this messing with hdparm was only 
> needed because of stupidity with the old IDE code (like DMA not being 
> automatically enabled if the low-level driver was built modular).

AFAIR there has never been such issue with IDE subsystem.

In modular case you just have to remember to _not_ load generic
IDE host driver if you don't need it, same with libata PATA.

Bart
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