Re: [dm-crypt] Wrong behavior?

From: Arno Wagner <arno@wagner.name>
To: dm-crypt@saout.de
Subject: Re: [dm-crypt] Wrong behavior?
Date: Wed, 14 Jul 2010 14:13:46 +0200	[thread overview]
Message-ID: <20100714121346.GA19846@tansi.org> (raw)
In-Reply-To: <1279109239.2415.10.camel@Koma-Station.localdomain>

The LUKS header is 1'052'672 bytes with default parameters.
See FAQ Item "What does the on-disk structure of LUKS look like?"
in section 5.

Arno

On Wed, Jul 14, 2010 at 02:07:19PM +0200, Sven Eschenberg wrote:
> Hi Milan,
> 
> thanks for the info and links. What I do not understand is this, I will
> use the easiest version for now:
> 
> cryptsetup luksFormat /dev/md125
> 
> And:
> 
> LUKS header information for /dev/md125
> 
> Version:       	1
> Cipher name:   	aes
> Cipher mode:   	cbc-essiv:sha256
> Hash spec:     	sha1
> Payload offset:	4096
> 
> But:
> 
> cat /sys/block/md125/queue/minimum_io_size 
> 524288
> 
> cat /sys/block/md125/queue/optimal_io_size 
> 1048576
> 
> whilst physical and logical blocksize are at 512 bytes.
> 
> I don't see why cryptsetup does not end up with 1024 sectors (which is
> the optimal_io_size) - or is the luks header bigger than 512k? even
> bigger than 1 MB (2048 sectors) ?
> 
> Regards
> 
> -Sven
> 
> 
> 
> 
> On Wed, 2010-07-14 at 13:52 +0200, Milan Broz wrote:
> > 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
> 
> 
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> http://www.saout.de/mailman/listinfo/dm-crypt
> 

-- 
Arno Wagner, Dr. sc. techn., Dipl. Inform., CISSP -- Email: arno@wagner.name 
GnuPG:  ID: 1E25338F  FP: 0C30 5782 9D93 F785 E79C  0296 797F 6B50 1E25 338F
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