[dm-crypt] Performance problems

Joakim Reinert mail at jreinert.com
Mon Nov 19 12:51:15 CET 2012


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Hello,

i intended to use dm-crypt + LUKS to encrypt my entire file system. I
ran into the following problem: After finishing cryptsetup i noticed
by testing with dd (dd if=/dev/zero of=/dev/mapper/cryptroot) with
different blocksizes, that i had read and write speeds of roughly
50MB/s. If you consider my setup, you will agree, that this is way too
slow:

cpu:        i7-2620 (AES-NI integrated)
disk:       Crucial m4 226GB SSD
ram:       4GB DDR-3 1333Mhz (Single Channel)

Additional information:

kernel:    linux 3.6.6.1
os:         arch linux

I have loaded the module aesni_intel and verified that the refcnt
changes in /proc/crypto when i open/close the encrypted partition.

I've already harrassed everybody at #archlinux and #crypto in IRC but
nobody seems to know what the problem might be. I also installed
truecrypt and did some benchmarks which show encryption and decryption
speeds of roughly 2GB/s.

Might this have something to do with the data alignment on disk? At
least with lvm it's suggested to define dataalignment=1m on SSD's. Is
it possible to define data alignment for dm-crypt?

Another possibility that would come to mind is a bug in the kernel.

I followed this guide to set up the encryption by the way:
https://wiki.archlinux.org/index.php/Dm-crypt_with_LUKS

Hoping to hear from you soon.

Kind regards

Joakim Reinert
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