linux-kernel - Re: ATA 4 KiB sector issues.

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Message-ID: <4B954224.6010208@zytor.com>
Date:	Mon, 08 Mar 2010 10:29:56 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	"Martin K. Petersen" <martin.petersen@...cle.com>
CC:	Tejun Heo <tj@...nel.org>,
	"linux-ide@...r.kernel.org" <linux-ide@...r.kernel.org>,
	lkml <linux-kernel@...r.kernel.org>,
	Daniel Taylor <Daniel.Taylor@....com>,
	Jeff Garzik <jeff@...zik.org>, Mark Lord <kernel@...savvy.com>,
	tytso@....edu, hirofumi@...l.parknet.co.jp,
	Andrew Morton <akpm@...ux-foundation.org>,
	Alan Cox <alan@...rguk.ukuu.org.uk>, irtiger@...il.com,
	Matthew Wilcox <matthew@....cx>, aschnell@...e.de,
	knikanth@...e.de, jdelvare@...e.de, Karel Zak <kzak@...hat.com>,
	Jim Meyering <jim@...ering.net>
Subject: Re: ATA 4 KiB sector issues.

On 03/08/2010 07:18 AM, Martin K. Petersen wrote:
> 
> Tejun> Partitioners maybe should only align partitions which will be
> Tejun> used by Linux and default to the traditional layout for others
> Tejun> while allowing explicit override.
> 
> I don't think we take the partition type into account.  Karel?
> 

We should not take the partition type into account.  The other aspect is
that FAT partitions need to be formatted differently to maintain the
alignment once set; I have recently contributed patches (which were
accepted) into mkdosfs to do the right thing there.

Looking at the Windows XP article, it looks like it is limited to
certain BIOSes; unfortunately it doesn't say what the particular BIOS
issue is.  If we can find a system which actually exhibits the bug it
might be possible to reverse-engineer a solution.

> Tejun> Reportedly, commonly used partitioners aren't ready to handle
> Tejun> drives larger than 2 TiB in any configuration and alignment isn't
> Tejun> done properly for drives with 4 KiB physical sectors.  4 KiB
> Tejun> logical sector support is broken in both the kernel 
> 
> Huh, what?  My homedir is on a 4KiB LBS/PBS drive and has been for ~2
> years.

For > 2 TiB drives with 4 KiB logical sectors and MS-DOS partition
tables, it is.

> Tejun> Unfortunately, the transition to 4 KiB sector size, physical only
> Tejun> or logical too, is looking fairly ugly.  Hopefully, a reasonable
> Tejun> solution can be reached in not too distant future but even with
> Tejun> all the software side updated, it looks like it's gonna cause
> Tejun> significant amount of confusion and frustration.
> 
> With regards to XP compatibility I don't think we should go too much out
> of our way to accommodate it.  XP has been disowned by its master and I
> think virtualization will take care of the rest.

I think that's is wildly optimistic, but I do observe there is a fix
from Microsoft in the article you reference.

> FWIW, recent fdisk has a command line flag that will enable/disable DOS
> compatible layout.

Yes, unfortunately it is still on by default.

	-hpa
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