FileVault Performance Compromise?

I can't comment on how Lion's FileVault 2 affects battery life, but I've had it running (Full Disk Encryption) on an older (2007) MacMini with 3GB of RAM for a few months, and it is a great solution for keeping a computer that might get stolen secure.

Beyond the initial encryption, which took a few hours, I really haven't noticed any performance difference. Given that this is an older machine, any negligible difference I might have missed would be even smaller on a newer machine like yours.

I was curious about this myself at the time and found this AnandTech article, which boils it down to a negligible CPU load, and a slight hit to your hard drive's throughput. They were using an SDD though, so the results may not exactly correspond with a spinning disk.

So if you're reading and writing to the disk a lot, you might notice a slight decrease in battery life as reads and writes will take a bit longer, but I doubt it'd be anything too drastic.

This depends on whether your MBP has an Intel processor which supports Intel® Advanced Encryption Standard (AES) which is also used in Filevault 2.

Ars Technica, published an extended review on Filvault 2 in Lion. They say:

Apple also leverages the special-purpose AES instructions and hardware on Intel's newest CPUs, further reducing the CPU overhead. The end result is that regular users will be hard-pressed to notice any reduction in performance with encryption enabled.

My experience

Hardware: Intel 2635QM (MBP early 2011) which supports AES encryption and Crucial M4 128GB SSD.

I'm downloading, listening to music, have several applications running, and SophosAV live scan enabled. My processor stats using iStat Pro: Idle 97%

• I have noticed a drop in read speeds of merely 4%.
• As the overall CPU load is nearly unchanged, the battery life is not affected significantly: In overall power consumption I will neglect the power drain of the SSD. The CPU and hard drive are the only significant factors that change the power consumption when disk encryption is enabled, I assume.

In answer to your question

See this list which compares all Intel processors used in the MBP released in 2010 (scroll to bottom, look for 'AES New Instructions'). Only four out of the six processors support AES instructions. However, it is possible that Apple did not choose to enable this functionality. This happened to my 2635QM. AES support was added later via a firmware update.