[dm-crypt] Wrong behavior?

Sven Eschenberg sven at whgl.uni-frankfurt.de
Wed Jul 14 14:07:19 CEST 2010


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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