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

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Message-ID: <20100317025101.GA13339@guarana.org>
Date:	Wed, 17 Mar 2010 13:51:01 +1100
From:	Kevin Easton <caf@...rana.org>
To:	James Bottomley <James.Bottomley@...e.de>
Cc:	linux-kernel@...r.kernel.org, Tejun Heo <tj@...nel.org>
Subject: Re: ATA 4 KiB sector issues.

James Bottomley wrote:
> On Wed, 2010-03-17 at 00:20 +0900, Tejun Heo wrote:

...

> > Well, the thing is that
> > 
> > * Anything remotely modern (>= XP) doesn't give a hoot about cylinder
> >   alignment.
> > 
> > * Anything older (<= 2000) is very likely to get confused with custom
> >   geometry starting from the BIOS itself.  For those cases, the only
> >   thing we can do is aligning partitions to cylinders abiding BIOS
> >   supplied geometry parameters which will usually be 255/63.
> > 
> > So, using custom geometry doesn't help compatibility at all.
> 
> Our partitioning tool still obey the integral cylinder rule ... we can
> argue about whether they should, but what we need is a strategy for
> fixing what is rather than what should be.

James / Tejun,

Can't we fix the problem by defaulting to aligning partitions to
start on an LBA that is a multiple of 64260 ?

Such partitions will always be 4KiB-aligned, *and* start-of-cylinder
aligned (assuming 255/63, as seems to be the norm).

Sure, that reduces your partition granularity to almost-32-MiB, but
that's pretty small potatoes these days (and it's only a *default*, so
you could always override that if you really cared, and didn't need 
the compatibility).

    - Kevin

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