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If I have a laptop, and I want to install an Ubuntu 11.04 on it, but disk performance would be an important thing, then how could I test the real differences between:

- not using encryption
- using luks/aes 128bit
- using luks/aes 256bit

So I would Install Ubuntu 3 times, I just not know how to do perf. test (good).

What programs/methods could be good for such io performance tests? (or it affects the CPU too? - software encryption! my cpu doesn't has aes-ni)

e.g.: I would install a minimal ubuntu iso, with no gui+run tests in single user mode

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Use a spare partition and a disk benchmark utility like bonnie++ to get a general feel for which systems take performance hits in what areas. You could also do a couple of identical installs in VirtualBox. Three machines with otherwise identical setups should take about 15 minutes of our time to setup with Ubuntu and by running them one at a time you should get a pretty level field to test between performance of your favorite apps, at least on a relative scale without implementing it system wide.

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As a rough estimate, since disk encryption requires the CPU to encrypt/decrypt each block, it means all data must pass through the CPU like old ATA PIO modes, effectively negating any advantage DMA transfers can give. So think of encryption as at least degrading your disk performance to ATA PIO mode. –  ultrasawblade Jul 3 '11 at 3:07
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