Re: ATA 4 KiB sector issues.

[James Bottomley]

On Tue, 2010-03-16 at 15:22 +0900, Tejun Heo wrote:
> Hello, James.
> 
> On 03/16/2010 03:14 PM, James Bottomley wrote:
> > So, it is true to say that picking a certain H/S geometry (which is
> > entirely withing the gift of the partitioner) will align msdos label
> > partitions, but will be don't care for all other labels: all other
> > partition labels (like gpt) use block as offset and don't have any truck
> > with the fictitious C/H/S stuff.
> 
> For any modern Linux and Windows, CHS simply doesn't matter.  They
> don't look at it at all.

If they have a msdos label, they do.

> > The big problem is that 99% of the x86 systems out there still use the
> > ancient msdos label for their boot disks, so aligning H/S going forwards
> > will give us a nice "just works" for x86 boxes.
> 
> What I don't get is that how picking up a custom geometry can make
> things work when there is *no* reliable way to determine which
> geometry was used during partitioning once the partitioning is
> complete.

For msdos labels, it's embedded in the label ... for all other labels,
it's made up on the spot.

>   Most BIOSs these days will simply report the geometry as
> being 255/63 regardless of the geometry used during partitioning.  So,
> how can using a custom geometry give that nice "just works" for x86
> boxes when nobody knows what geometry is in use?

Because the msdos label can only partition in units of cylinders.  If
you're using an msdos label, picking the right H/S gets you alignment.

James


--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/