I've gotten a few eMails complaining that it takes a huge tool on some users computer performance while recording pc game-play. I cannot speak for any other recording software except Fraps because that's all I use.
Fraps records video and audio unencoded, uncompressed, raw. That means the files are huge. 30 minutes of recorded gameplay footage are about 50-70 gigabyte large, and there's absolutely no way around that. Which brings me to my first point of this how-to: get a large HDD/SSD. I'm talking about 1 single HDD/SDD, specifically just for Fraps. 250 Gigabyte ought to do it. Recording video and audio uncompressed also means a huge tool on your computer initially.
Now, the trick is to set up your system in a way that Fraps, while recording, takes as little a tool as possible on your running game.
I have 3 HDDs. 1st HDD is partitioned in C, F, G. 2nd HDD is partitioned in E, H and 3rd HDD is unpartitioned, D. C is my System partition, H is my games partition and D is my Fraps HDD.
You see, 1 HDD for my system, 1 HDD for my games, 1 HDD for Fraps. They are all physically separated, which is imperative. Why am I doing it this way? When a game runs the read/write heads goes back and forth reading the game and deploying the data to your CPU/RAM/GPU. When Fraps records it causes the read/write heads to move around and write data on the HDD.
Now imagine you have a game running and Fraps recording on the same HDD/partition. That means the read/write head has to do double the work namely reading the game and writing the recording (in simplified terms, realistically it's more than double the work) on the HDD which in turn translates into FPS drops and "lags" in the game. And remember, recording uncompressed with Fraps already takes a huge tool on your computer.
So ideally you'd want your game running on one HDD and Fraps recording on another, physically separated, (unpartitioned) HDD. Another important point is the swap/page file. Make absolutely sure your swap/page file is not on the same HDD as Fraps or your games are. I've my swap/page file stowed on C: .
It took me a bit experimenting back then but all this lead to a more stable, even increased, FPS while a massive drop in "lags". It may not work for each and every one of you, but it did for me.
On a side note: Perhaps some of you are using SSDs and can share your experiences? I don't have a SSD, yet, so I can't say how well it works on SSDs.