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SubjectRe: [dm-devel] Re: [PATCH 1/3] block: add alt_size
Konrad Rzeszutek wrote:
> .. snip ..
>>> Also, values with magic block counts, while there is no way to get the
>>> blocksize with the same interface, are pretty weird. I think the
>>> current "size" attribute is just a bug.
>> Logical block size is fixed at 512 bytes. Offset and size are always
>> represented in multiples of 512 bytes and only get converted to
>> hardware block size in the lld.
>
> That interpretation is at odds with the work that Martin Peterson is
> doing with the 4K support. In the e-mail titled: "Re: [PATCH 4 of 8] sd:
> Physical block size and alignment support",
> Message-ID:<yq1ab67b51p.fsf@sermon.lab.mkp.net> he says:
>
> "
> Konrad> about what a 'logical block', and 'physical block' is
> Konrad> vs. 'hardware sector' ?
>
> Well, another item on my todo list is to kill the notion of hardware
> sector completely. The protocols have been referring to logical blocks
> for ages.
>
> It hasn't been a big problem until now because logical block size has
> been equal to the hardware sector size. That's no longer a valid
> assumption.
> "
>
> Are the ATA/SCSI/etc specs at odds with each other about this?

Hardware specs aren't of concern here. The logical block concept is
there simply to give 9 bit addressing advantage, nothing more, nothing
less. If hardware's sector size doesn't match it, the lld should be
mapping the sector addresses and sizes and cdrom and a few other
drives have been doing that for ages. There's nothing new about
devices with sectors larger than 512 bytes.

Thanks.

--
tejun


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