[dm-crypt] Alignment issue with 4K disk

Milan Broz gmazyland at gmail.com
Sat Jan 9 13:30:37 CET 2016



On 01/07/2016 07:00 PM, .. ink .. wrote:
> There is another (i think) related problem that was reported here[1]
> 
> Are these warnings serious or can they be ignored?
> 
> 
> [1] https://github.com/mhogomchungu/zuluCrypt/issues/25

If I read this correctly, it s caused by mapping of an unaligned plaintext device-mapper
device (unlocked VeraCrypt) to underlying partition.

That's a bug (or lack of proper alignment) inside VeraCrypt header or in GPT partitioning
- it should respect underlying device alignment while creating device/partition.

Anyway, I think the only consequence should be performance drop, it should still work.

Note that output from GPT says 512B while dm kernel message says 4k block... GPT should
use 4k block as well.
Reporter should paste output of "lsblk -t" with device activated to check what underlying
device report alignment limits are violated in storage stack).

We cannot do anything with it I guess, cryptsetup just activates what is written inside
Veracrypt header using alignment limits reported by kernel.

Milan


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