linux-kernel - Re: [dm-devel] Re: [PATCH 1/3] block: add alt

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Message-ID: <4A08C871.9000100@kernel.org>
Date:	Tue, 12 May 2009 09:53:05 +0900
From:	Tejun Heo <tj@...nel.org>
To:	Konrad Rzeszutek <konrad@...tualiron.com>
CC:	device-mapper development <dm-devel@...hat.com>,
	Kay Sievers <kay.sievers@...y.org>, jeff@...zik.org,
	linux-scsi@...r.kernel.org, Mauelshagen@...hat.com,
	linux-kernel@...r.kernel.org, linux-ide@...r.kernel.org,
	jens.axboe@...cle.com, martin.petersen@...cle.com
Subject: Re: [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@...mon.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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