[dm-crypt] Alignment issue with 4K disk

Sven Eschenberg sven at whgl.uni-frankfurt.de
Mon Jan 4 22:54:52 CET 2016


Hi,

start=4194304 -> assumind this is in 512 byte blocks, the start sector 
is aligned to MByte boundary and thus 4k boundary.

Anyway, if your device only has one partition which is encrypted with 
dm-crypt, set it up to start at sector 2048 (which should be default for 
parted, fdisk and so on). Pass align-payload 2048 during creation of the 
LUKS header, which will give you an MByte boundary and should always be 
okay.

If the kernel still complains, then something else might be going wrong.

Regards

-Sven



Am 04.01.2016 um 22:31 schrieb Yves-Alexis Perez:
> Hi,
>
> I'm trying to setup an encrypted volume on an external disk which has 4k
> physical sector size (with 512b logical sector size).
>
> I've used various parted option (-a none / minimal / optimal) and various --
> align-payload options to cryptsetup, but everytime I luksOpen the container, I
> get a kernel log with:
>
> janv. 04 22:25:04 scapa kernel: device-mapper: table: 253:4: adding target device sdb1 caused an alignment inconsistency: physical_block_size=4096, logical_block_size=512, alignment_offset=0, start=4194304
>
> (argument for start= changes for different values of the --align-payload)
>
> I'm not sure it's really serious, but any idea how to fix that?
>
> Regards,
>
>
>
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