You must be doing something wrong then. Do you have a PS2 Classic with an adapter or a PS2 Slim? What revision? What method? Are you using complete dumps? Are they clean or patched? OpenPS2Loader or HDLoader? There's a whole procedure, you see.
Loading from USB has a very small compatibility list, lags during fmv due to the painfuly slow speed of the USB slot (1.1 revision of USB) and loads forever, it should only be regarded a last resort or a homebrew-loading method. Describe your issue and answer my questions and I may help you out - buying an external drive for this purpose is equal to throwing your money away when there are better, cheaper alternatives.
I own a ps2 fat and both of my games are clean and patch the purpose of playing games on the hard drive is that I don't really wanna damage my laser since I played burned ps2 games it was working very well but I know that It can break my laser. some of the people got their laser broken even though they burn it correctly and got a good blank disk.