[dm-crypt] Reconsidering default options for cryptsetup-reencrypt

Sven Eschenberg sven at whgl.uni-frankfurt.de
Sat Nov 24 18:01:11 CET 2012


On Fri, November 23, 2012 07:07, Arno Wagner wrote:
> On Fri, Nov 23, 2012 at 05:12:35AM +0100, Karol Babioch wrote:
>> Hi,
>>
>> I'm currently reencrypting my (hardware) RAID setup, which is quite big
>> (12 TB) in order to change the cipher from aes-xts-plain to
>> aes-xts-plain64.
>>
>> While playing around with various options, I found out that a block size
>> of 64 MB and the use of direct I/O results in the highest speed for me.
>
> This seems to be RAID options (i.e. out-of-scope for cryptsetup), and
> very specific ones as you have some hardware RAID solution. Also 64MB
> block size is very, very large and will be a problem for some workloads.
>
>

On a side note, most HW Raids do not provide IO hinting, even worse, as a
result the IO hinting is wrong, which has an impact on alignment etc.,
esp. when it boils down to something special like 4k sector drives. If the
RAID stripes are not aligned to the 4k boundaries of the drive, and
dmcrypt cannot align to the 4k boundary as well as the stripe size, you
will suffer a strong degradation in performance.

BTW, what exactly are you referring to, when you talk about 64 MB blocksize?


>
> [...]
>
> Arno
>
> --
> Arno Wagner,     Dr. sc. techn., Dipl. Inform.,    Email: arno at wagner.name
> GnuPG: ID: CB5D9718  FP: 12D6 C03B 1B30 33BB 13CF  B774 E35C 5FA1 CB5D
> 9718
> ----
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-Sven




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