[dm-crypt] unusual writing speeds when benchmark speeds are high enough

Matthias Schniedermeyer ms at citd.de
Sun Mar 17 23:55:16 CET 2013


On 17.03.2013 17:36, .. ink .. wrote:
> Sorry for my previous email without a title,resending the email with a
> title this time.
> 
> A user of cryptsetup(through zuluCrypt) asked me a question i can not
> answer and asking it here.
> 
> In his system,"cryptsetup benchmark" gives the following results:
> 
> [root <at> sheep 13] ~ > cryptsetup benchmark
> # Tests are approximate using memory only (no storage IO).
> PBKDF2-sha1       341333 iterations per second
> PBKDF2-sha256     193607 iterations per second
> PBKDF2-sha512      64125 iterations per second
> PBKDF2-ripemd160  303758 iterations per second
> PBKDF2-whirlpool   64125 iterations per second
> #  Algorithm | Key |  Encryption |  Decryption
>      aes-cbc   128b   183,6 MiB/s   215,4 MiB/s
>  serpent-cbc   128b    68,0 MiB/s    68,9 MiB/s
>  twofish-cbc   128b   167,7 MiB/s   177,5 MiB/s
>      aes-cbc   256b   142,3 MiB/s   161,5 MiB/s
>  serpent-cbc   256b    69,7 MiB/s    67,0 MiB/s
>  twofish-cbc   256b   170,1 MiB/s   177,8 MiB/s
>      aes-xts   256b   201,2 MiB/s   205,6 MiB/s
>  serpent-xts   256b    69,7 MiB/s    67,6 MiB/s
>  twofish-xts   256b   180,5 MiB/s   175,6 MiB/s
>      aes-xts   512b   147,0 MiB/s   152,5 MiB/s
>  serpent-xts   512b    70,5 MiB/s    67,8 MiB/s
>  twofish-xts   512b   182,0 MiB/s   176,0 MiB/s
> 
> The system is decent enought.
> 
> The write speed he is getting though through the mapper is unusually
> slow,the test is below:
> 
> 
> [root <at> sheep 8] ~ > dd if=/dev/zero of=test.img bs=70M count=1
> 1+0 Datensätze ein
> 1+0 Datensätze aus
> 73400320 Bytes (73 MB) kopiert, 2,58497 s, 28,4 MB/s
> 
> [17.03.2013 21:50 Uhr]
> [root <at> sheep 9] ~ > cryptsetup create test test.img
> Passsatz eingeben:
> 
> [17.03.2013 21:51 Uhr]
> [root <at> sheep 10] ~ > dd if=/dev/zero of=/dev/mapper/test bs=10M count=1
> 1+0 Datensätze ein
> 1+0 Datensätze aus
> 10485760 Bytes (10 MB) kopiert, 67,2014 s, 156 kB/s
> 
> [17.03.2013 21:52 Uhr]
> [root <at> sheep 11] ~ > cryptsetup remove test
> 
> As the test show,He is getting 156kB/s when using dd over the encryption
> mapper verses 28MB/s when using dd straight.

dd was with conv=fsync?
Otherwise you are measuring buffer cache.

> Where is the wrong in his system? version of cryptsetup used is 1.6.0

I would say, there are quite a few details missing.
Hardware, Software?
28.4 MB/s also isn't what i would call fast, what is that?



-- 

Matthias


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