Matthew McGiffen answers an age-old question:
Microsoft states that enabling TDE usually has a performance overhead of 2–4%. That doesn’t sound like very much, and personally I wouldn’t let it bother me if I want to make sure my data is encrypted at rest. However, you may have heard other sources saying that it’s actually a lot more than that – and the performance impact is a high price to pay for the level of protection offered. So, what’s the truth?
It turns out the answer is a bit more complex than simply saying “x%,” though as a first approximation, I’d still say that the 2-4% is a good starting point. For what would move you off of that 2-4%, read the whole thing.