From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <mbroz@redhat.com>
Received: from mx1.redhat.com (mx1.redhat.com [209.132.183.28])
	by mail.saout.de (Postfix) with ESMTP
	for <dm-crypt@saout.de>; Wed, 14 Jul 2010 13:52:56 +0200 (CEST)
Message-ID: <4C3DA515.4030909@redhat.com>
Date: Wed, 14 Jul 2010 13:52:53 +0200
From: Milan Broz <mbroz@redhat.com>
MIME-Version: 1.0
References: <1279054281.867.5.camel@Koma-Station.localdomain>	
	<4C3CD6C8.6020303@redhat.com>	
	<1279059451.867.23.camel@Koma-Station.localdomain>	
	<4C3D6E0D.6020802@redhat.com>
	<1279107557.2415.3.camel@Koma-Station.localdomain>
In-Reply-To: <1279107557.2415.3.camel@Koma-Station.localdomain>
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 7bit
Subject: Re: [dm-crypt] Wrong behavior?
List-Id: <dm-crypt.saout.de>
List-Unsubscribe: <http://www.saout.de/mailman/options/dm-crypt>,
	<mailto:dm-crypt-request@saout.de?subject=unsubscribe>
List-Archive: <http://www.saout.de/pipermail/dm-crypt>
List-Post: <mailto:dm-crypt@saout.de>
List-Help: <mailto:dm-crypt-request@saout.de?subject=help>
List-Subscribe: <http://www.saout.de/mailman/listinfo/dm-crypt>,
	<mailto:dm-crypt-request@saout.de?subject=subscribe>
To: Sven Eschenberg <sven@whgl.uni-frankfurt.de>
Cc: dm-crypt@saout.de

On 07/14/2010 01:39 PM, Sven Eschenberg wrote:

> Is there any 'easy' way to access this information. specifically I am
> interested, why md would report a 6144 sectors alignment on my 4 disk
> raid5 with 512 kb chunks instead of 3072.

Values are in in sysfs also, I am just using topology ioctl which is simpler.

sysfs interface
---------------
/sys/block/<disk>/alignment_offset
/sys/block/<disk>/<partition>/alignment_offset
/sys/block/<disk>/queue/physical_block_size
/sys/block/<disk>/queue/logical_block_size
/sys/block/<disk>/queue/minimum_io_size
/sys/block/<disk>/queue/optimal_io_size

cryptsetup uses minimal/optimal io_size and alignment value
to calculate payload offset.

A lot of info here:

http://people.redhat.com/msnitzer/docs/io-limits.txt
https://ata.wiki.kernel.org/index.php/ATA_4_KiB_sector_issues

Milan