My external drive works great for audio (although I haven't pushed the track count).
It's a Seagate 160 with dual Firewire 400 / USB 2.0 interfaces. I bought a (slightly pricey) product rather than build my own because the Seagate is particularly quiet and rugged, and I use it for live recordings. (Thinkpad, MBox using USB 1.1, HD connected to Firewire 400 PC Card)
You might think USB 2.0 will move the data faster (480 Mb/s for USB 2.0 vs. 400 Mb/s for Firewire 400), but that's not the case.
Firewire is a more efficient protocol (and also uses way fewer cycles on your host CPU) .
I've measured throughput on both interfaces (I'm pretty geeky
) and Firewire 400 moves data almost 3x faster than USB 2.0 . (About 27-30 MB/sec vs. ~11-13 MB/sec for USB, if I recall correctly). This was using a 2.8G P4 system with 1M RAM, with both USB 2.0 and Firewire interfaces. I also use the external drive to back up systems used my wife and daughters, and backups take a lot less time when I use Firewire.
Bottom line: both USB 2.0 and Firewire 400 will work fine, but if you're pushing track count (or want to reduce host CPU load), Firewire will perform better.
YMMV, as always
- Jim