From: H. Peter Anvin on
On 03/09/2010 04:14 PM, Daniel Taylor wrote:
>
> The MBR in a GPT installation doesn't map the first GPT partition, it maps
> the entire drive
> drive after the first sector, as well as marking it type 0xEE. The start
> LBA of the file system
> is not correctly located in the MBR.
>
> I will run some experiments to see if any of the systems on my desk can boot
> Linux from a GPT.

There is something called a "hybrid MBR", which is basically a GPT disk
with a single partition (the current bootable partition) mapped as an
MBR partition, instead of marking the whole disk 0xEE.

-hpa
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From: Mark Lord on
On 03/09/10 19:00, Tejun Heo wrote:
> On 03/09/2010 10:55 PM, Mark Lord wrote:
>> On 03/07/10 22:48, Tejun Heo wrote:
>> ..
>>> Please note that hdparm is misreporting the alignment offset. It
>>> should be reporting 512 instead of 256 for offset-by-one drives.
>> ..
>>
>> That issue was fixed quite a while ago.
>> Upgrade your elderly copy of hdparm.
>
> Heh heh, *you* were keeping it from me! Anyways, is there hdparm
> devel tree published somewhere? I wandared the SF page for quite a
> bit (which for some reason is very difficult to find things in) but I
> couldn't find one. If it's not, it might be a good idea to put it on
> SF or git.kernel.org?
...

No tree. There's just my working copy (private),
and the published versions at SF.

But yes, SF has gotten incredibly more cryptic to use of late,
and I might have to move it somewhere more accessible soon.

Cheers!
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From: Gabor Gombas on
On Tue, Mar 09, 2010 at 04:14:30PM -0800, Daniel Taylor wrote:

> I will run some experiments to see if any of the systems on my desk can boot
> Linux from a GPT.

My desktop with a BIOS from 2005 has no problems with GPT. AFAIK a
recent Debian installer automatically chooses GPT if the disk is 2 TB or
larger.

Gabor
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From: Matthew Wilcox on
On Mon, Mar 08, 2010 at 10:41:57AM -0500, Martin K. Petersen wrote:
> What I meant to say was that I know ATA supports 4 KB LBS and that
> nobody appears to care about it.

I sent patches to add support ... they were ignored.

Part of the problem is that ATA is heinously broken wrt non-512 byte
sector sizes. You have to know which commands work in multiples of
the block size, and which commands work in multiples of 512-bytes.
There's no easy way to figure it out; you need a table.

--
Matthew Wilcox Intel Open Source Technology Centre
"Bill, look, we understand that you're interested in selling us this
operating system, but compare it to ours. We can't possibly take such
a retrograde step."
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From: Denys Vlasenko on
On Wed, Mar 10, 2010 at 12:46 AM, Arnd Bergmann <arnd(a)arndb.de> 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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