performance of dm-crypt devices?

I just set up an encrypted LUKS device using the information on http://www.saout.de/tikiwiki/tiki-index.php?page=EncryptedDeviceUsingLUKS

There was a suggestion there, which prompted me to check the performance:

If you wish, use /sbin/hdparm to benchmark. However my benchmarks on an AMD Athlon 3200 indicate no great difference between an encrypted and a normal unencrypted partition.

First, I set read-ahead to the same value on both devices (original LVM device, and the crypted one):

# blockdev --setra 16384 /dev/mapper/crypttest
# blockdev --setra 16384 /dev/mapper/san1-test

Next, hdparm test:

# hdparm -t mapper/crypttest mapper/san1-test

mapper/crypttest:
Timing buffered disk reads: 116 MB in 3.01 seconds = 38.54 MB/sec
HDIO_DRIVE_CMD(null) (wait for flush complete) failed: Inappropriate ioctl for device

/dev/san1/file1-swap:
Timing buffered disk reads: 304 MB in 3.12 seconds = 97.46 MB/sec
HDIO_DRIVE_CMD(null) (wait for flush complete) failed: Inappropriate ioctl for device

So, this quick test suggests that with a crypted device, I get about 40% performance of the original LVM volume?

My setup is hardware RAID-10, and a dual core 3 GHz Xeon.

Is it normal? I would say yes, as both cores use 100% CPU when I do intensive reads from an encrypted volume.
However, this seems to contradict with "However my benchmarks on an AMD Athlon 3200 indicate no great difference between an encrypted and a normal unencrypted partition".

I used aes-cbc-essiv:sha256 cipher.

Perhaps, I should use something lighter?

Tomasz Chmielewski
http://wpkg.org

Ouch, I guess there is a better list for such questions, like dm-crypt... Sorry for noise. Will repost it there.

Tomasz Chmielewski
http://wpkg.org