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

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Date:	Thu, 11 Mar 2010 20:35:26 +0530
From:	Nikanth Karthikesan <knikanth@...e.de>
To:	James Bottomley <James.Bottomley@...e.de>
Cc:	Theodore Tso <tytso@....edu>,
	Damian Lukowski <damian@....rwth-aachen.de>,
	"linux-ide@...r.kernel.org" <linux-ide@...r.kernel.org>,
	Jeff Garzik <jeff@...zik.org>, Matthew Wilcox <matthew@....cx>,
	"Martin K. Petersen" <martin.petersen@...cle.com>,
	Tejun Heo <tj@...nel.org>, lkml <linux-kernel@...r.kernel.org>,
	Daniel Taylor <Daniel.Taylor@....com>,
	Mark Lord <kernel@...savvy.com>,
	"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,
	aschnell@...e.de, jdelvare@...e.de
Subject: Re: ATA 4 KiB sector issues.

On Thursday 11 March 2010 20:09:34 James Bottomley wrote:
> On Thu, 2010-03-11 at 09:28 -0500, Theodore Tso wrote:
> > On Mar 11, 2010, at 8:57 AM, Nikanth Karthikesan wrote:
> > > I guess, what he meant was, to keep filesystem blocks aligned, even if
> > > the partition is not. Say if the partition is mis-aligned by 512-bytes,
> > > let the filesystem waste 4k-512bytes and keep it's blocks aligned. But
> > > it might be a case of over-engineering, possibly requiring disk format
> > > change.
> >
> > Ah, yes, I agree with you; that's probably what he meant.
> >
> > Sure, that's theoretically possible, but it would mean changing every
> > single filesystem, and it would require a file system format change
> > --- or at least a file system format extension.
> >
> > It would seem to be way easier to simply fix the partitioning tools to
> > do the right thing, though.
> 
> Actually, it's a layering violation.  The filesystem shouldn't need to
> probe the device layout ... particularly when there are complexities
> like is it logical 512 or physical, and if logical 512 on 4k does it
> have an offset exponent or not.
> 
> We can transmit certain abstractions of information up the stack (like
> stripe width for RAID arrays which should be the fs optimal write size),
> but for this type of alignment, which can be completely solved at the
> partition layer, the information should really stay there and the
> filesystem should "just work".
> 

Right. It would be layering violation and we have LVM to solve it already.

The real problem, here is just that partitioning-tools should create 
partitions that can work with both XP as well as Windows7. May be distro 
installers, should ask the user which compatibility he needs.

Thanks
Nikanth
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