Re: ATA 4 KiB sector issues.

[Denys Vlasenko]

On Wed, Mar 10, 2010 at 12:46 AM, Arnd Bergmann <arnd@xxxxxxxx> wrote:
> On Monday 08 March 2010 04:48:35 Tejun Heo wrote:
>> Unfortunately, while Windows can assume that newer releases won't
>> share the hard drive with older releases including Windows XP, Linux
>> distros can't do that.  There will be many installations where a
>> modern Linux distros share a hard drive with older releases of
>> Windows.  At this point, I can't see a silver bullet solution.
>>
>> Partitioners maybe should only align partitions which will be used by
>> Linux and default to the traditional layout for others while allowing
>> explicit override.  I think Windows XP wouldn't have problem with
>> differently aligned partitions as long as it doesn't actually use them
>> but haven't tested it.
>
> Any idea if XP can cope with partition tables that use a 32-sector, 128-head
> geometry rather than the default 63-sector, 255-head one? That seems to
> be what some flash memory cards are using and it would make any cylinder
> aligned partition also 4096-byte aligned, at the cost of moving the
> 1024-cylinder boundary from 7.88 GiB to 2 GiB.
>
> Do we know of anything that requires 63s/255h?

63s/255h is more or less "standard" now.

Alignment issues can be solved by picking a good multiple of
_heads_ or _cylinders_:

For first partition, pick the start at 8th head:

cyl 0 head 1 sector 1: LBA sector 63) - bad
cyl 0 head 8 sector 1: LBA sector 8*63) - good (4k aligned)

For any other partition, pick start cylinder which is a multiple of 8:

cyl 8*x head 0 sector 1: LBA sector 8*x*255*63 - good (4k aligned)

This will actually work well for *any* geometry, not only for 63s/255h.
-- 
vda
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