Just like the recording feature in the mac version of WoW, the most important aspect to recording video on FRAPS is
how fast you can write data to a hard drive; the other parts just apply to if you want to record video with higher settings in the game. Depending on your resolution, even one external drive can't have the write speed to maintain a decent FPS. Terraburn stated that the best way to record with FRAPS(and the Mac client) is to a drive that isn't used by WoW and in a RAID setup. These numbers are from my mac client for the data rate at recording video @ 1280x800 vs. 1920x1200 but should be the same for FRAPS:
20FPS: 29/66mb/s
25FPS: 37/83mb/s
30FPS: 44/99mb/s
60FPS: 88/198mb/s
At 1280x800, you could record to the same HD as WoW but it would kill your FPS in game. With my Macbook, I tested out the highest FPS by recording to an external HD connected by eSATA since the mac client has an automatic disable feature if the write speed isn't high enough(~70mb/s) and I can only record up to 20fps at my resolution of 1920x1200. Anything faster and I'd need something like WD Raptors or SSD's in RAID0
