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Date:	Thu, 07 Aug 2014 18:40:46 +0300
From:	Boaz Harrosh <>
To:	Karel Zak <>
CC:	Boaz Harrosh <>,
	Ross Zwisler <>,
	Jens Axboe <>,
	Matthew Wilcox <>,
	linux-kernel <>,
	linux-fsdevel <>
Subject: Re: [PATCH 4/4] brd: Request from fdisk 4k alignment

On 08/07/2014 06:21 PM, Karel Zak wrote:
>  fdisk uses physical sector size or minimal I/O size (greater value wins)


>> I was trying to play with the  heads, sectors, cylinders; values but none I tried
>  don't play with CHS, that's waste of time and it's completely ignored
>  by fdisk by default
>> would cause an alignment of 4k, not even of the first partition start.
>> Please advise what I can do?
>  IMHO you're right with your patch (alignment offset is IMHO bad way).
>  It's all (brd) about pages, is there any reason to use something else
>  for I/O limits?
>  It would be also nice to set minimal and optimal io size, zero values
>  in this case means (for userspace) that the device does not provide
>  any I/O information to system. It's normal for old hw disks and then
>  we use some built-in defaults, but I don't see a reason to do the
>  same for virtual devices. 

Hi Ross

I have by now read the all code, and Karel also confirms this from fdisk
side. The best for us is the use of "physical sector size" but with
our "minimal I/O size" set to 512. The later has actual bad effects in
the Kernel code itself. But the "physical sector size" has no effect on
Kernel code, and actually has a very good affect on fdisk which now works
the way we would like it.

Please send your review-by so Jens can pick these up for mainline

>     Karel


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