[dm-crypt] Alignment issue with 4K disk

Sven Eschenberg sven at whgl.uni-frankfurt.de
Sun Jan 10 02:14:02 CET 2016


Hi Eugen,

Indeed the optimal IO value (on sdc) seems a little weird. Yet this 
should not create any alignment warnings.

zuluCrypt-1001-NAAN-sdc4-1790378342: 0 11406264975 - Now this is not 4k 
aligned (sectors must be divideable by 8 to be 4k aligned). Indeed the 
encrypted payload should start at 11406264976 sectors, so there is a -1 
sector misalignment (See lsblk output saying so). VeraCrypt did not 
properly align the payload when the container was created, I assume.

Regards

-Sven


Am 10.01.2016 um 01:25 schrieb Eugen Rogoza:
> Hi,
>
>> Reporter should paste output of "lsblk -t" with device activated to check what underlying
>> device report alignment limits are violated in storage stack).
>
> I am the reporter and the output of 'lsblk -t' with encrypted partition mounted is below. sda2 is the one that works fine, sdc4 is the one that throws alignment warnings.
>
> root at nuc:~> lsblk -t
> NAME                                    ALIGNMENT MIN-IO   OPT-IO PHY-SEC LOG-SEC ROTA SCHED RQ-SIZE  RA WSAME
> sda                                             0   4096        0    4096     512    1 cfq       128 128    0B
> ├─sda1                                          0   4096        0    4096     512    1 cfq       128 128    0B
> └─sda2                                          0   4096        0    4096     512    1 cfq       128 128    0B
>    └─zuluCrypt-1001-NAAN-sda2-4071757814         0   4096        0    4096     512    1           128 128    0B
> sdb                                             0    512        0     512     512    0 noop      128 128    0B
> ├─sdb1                                          0    512        0     512     512    0 noop      128 128    0B
> ├─sdb2                                          0    512        0     512     512    0 noop      128 128    0B
> ├─sdb3                                          0    512        0     512     512    0 noop      128 128    0B
> └─sdb4                                          0    512        0     512     512    0 noop      128 128    0B
> sdc                                             0   4096 33553920    4096     512    1 cfq       128 128   32M
> ├─sdc1                                          0   4096 33553920    4096     512    1 cfq       128 128   32M
> ├─sdc2                                          0   4096 33553920    4096     512    1 cfq       128 128   32M
> ├─sdc3                                          0   4096 33553920    4096     512    1 cfq       128 128   32M
> └─sdc4                                          0   4096 33553920    4096     512    1 cfq       128 128   32M
>    └─zuluCrypt-1001-NAAN-sdc4-1790378342        -1   4096        0    4096     512    1           128 128    0B
>
>
>
>> That is indeed true and further info including 'dmsetup table' will be
>> necessary to tell what is really going on.
>
> Output below. Again, sdc4 is the problematic one.
>
> root at nuc:~> dmsetup table
> zuluCrypt-1001-NAAN-sdc4-1790378342: 0 11406264975 crypt aes-xts-plain64 00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000 256 8:36 256
> zuluCrypt-1001-NAAN-sda2-4071757814: 0 1324371456 crypt aes-xts-plain64 00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000 256 8:2 256
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