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SubjectRe: ATA 4 KiB sector issues.
> S-2. The proper solution.
>
> Correct alignments for all partitions can't be achieved by the
> firmware alone. The system utilities should be informed about the
> alignment requirements and align partitions accordingly.
>
> The above firmware workaround complicates the situation because the
> two different configurations require different offsets to achieve
> the correct alignments. ATA/ATAPI-8 specifies a way for a drive to
> export the physical and logical sector sizes and the LBA offset
> which is aligned to the physical sectors.
>
> In Linux, these parameters are exported via the following sysfs
> nodes.
>
> physical sector size : /sys/block/sdX/queue/physical_block_size
> logical sector size : /sys/block/sdX/queue/logical_block_size
> alignment offset : /sys/block/sdX/alignment_offset
>
> Let the physical sector size be PSS, logical sector size LSS and
> alignment offset AOFF. The system software should place partitions
> such that the starting LBAs of all partitions are aligned on
>
> (n * PSS + AOFF) / LSS
>
> For 4 KiB physical sector offset-by-one drives, PSS is 4096, LSS 512
> and AOFF 3584 and with n of 7 the above becomes,
>
> (7 * 4096 + 3584) / 512 == 63
>
> making sector 63 an aligned LBA where the first partition can be
> put, but without the offset-by-one mapping, AOFF is zero and LBA 63
> is not aligned.
>
> With the above new alignment requirement in place, it becomes
> difficult to honor the legacy one - first partition on sector 63 and
> all other partitions on cylinder boundary (255 * 63 sectors) - as
> the two alignment requirements contradict each other. This might be
> worked around by adjusting how LBA and CHS addresses are mapped but
> the disk geometry parameters are hard coded everywhere and there is
> no reliable way to communicate custom geometry parameters.

Hello,
I have practically no knowledge of Linux' block device drivers,
but is this really a partitioning issue? I think the problem is
with the filesystems when clustering multiple blocks without
knowledge of the sector alignment and sector size of the underlying
block device. Maybe it is a better solution to adapt the filesystem
buffer routine which reads/writes data from/to the block device?

Best regards
Damian


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