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

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Message-ID: <yq1zl2ic058.fsf@sermon.lab.mkp.net>
Date:	Mon, 08 Mar 2010 10:18:27 -0500
From:	"Martin K. Petersen" <martin.petersen@...cle.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	"linux-ide\@vger.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, "H. Peter Anvin" <hpa@...or.com>,
	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.

>>>>> "Tejun" == Tejun Heo <tj@...nel.org> writes:

Tejun> The [Windows Vista/7] partitioner seems to be using 1M as the
Tejun> basic alignment unit and offsetting from there if explicitly
Tejun> requested by the drive

Yep.

Tejun> Please note that hdparm is misreporting the alignment offset.  It
Tejun> should be reporting 512 instead of 256 for offset-by-one drives.

Already fixed.  Your hdparm must be old.

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?

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.

Tejun> (need more details and probably a whole section on partitioner
Tejun> behaviors)

I'm Cc:'ing Karel Zak and Jim Meyering who have been doing all the
alignment work for fdisk and parted respectively.  Karel, Jim: The full
writeup is here:

	http://ata.wiki.kernel.org/index.php/ATA_4_KiB_sector_issues

It'd be great if you guys could share what you have been doing to the
tooling.

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.

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

-- 
Martin K. Petersen	Oracle Linux Engineering
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