On Tue, 9 Mar 2010, Tejun Heo wrote:
Hello,
I prefer if linux-ide@xxxxxxxxxxxxxxx is cc'd so if you're okay with
it, please add cc when you reply.
OK.
On 03/08/2010 05:53 PM, Tomasz Palac wrote:
I've read your document on ATA 4 KiB sector issues and I have a simple
solution for partitioning 4 KiB physical/512 B logical drives with no
offset.
I use geometry of 64 heads and 32 (logical) sectors. This way cylinder
is exactly 1 MiB. First partition starts at 2nd cylinder and is aligned
at 1 MiB. Other primary partition are aligned at 1 MiB too. If one of
them is extended partition, then logical partitions within it will be
aligned at 16 KiB (32 logical sectors).
This scheme can be applied to SSDs, with the exception of logical
partitions (16 KiB alignment will probably not be enough).
I don't know if older Windows will accept such partitioning scheme, but
if it uses CHS values, then it should.
Well, the thing is that there is no way to reliably communicate those
geometry values and 255*63 is hardcoded everywhere. The only way you
can deduce the geometry is by solving equation with the CHS address
and LBA in the partition table but for that to work the first
partition should end before CHS limit.
This limit is 8 GiB and there is no problem with first partitions
extending beyond that. This is because such partitions are described in
partition table as ending at 1023/255/63 (or something like that). Real
size of partition is specified by LBA values.
Using custom geometry is a good way to trick a partitioner which
partitions based on CHS alignment to align to larger units but it
isn't meaningful outside of that. If CHS dosen't follow 255*63, a lot
of code (firmware, BIOS, boot loader, OS...) will just assume CHS is
incorrect.
As of firmware, Large Disk Howto states that a lot of SCSI host adapters
are using 64/32 geometry (at least for disks smaller than 8 GiB). If BIOS
supports EDD (INT13h Extensions), then disk geometry is irrelevant. If
not, then geometry can be read from partition table. The only problem with
64/32 geometry is 1 GiB (as opposed to 8 GiB) limit for boot partition
(without using EDD). The same applies to boot loaders. Modern OSes don't
use CHS.
--
Tomasz Palac, AGH University of Science and Technology
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