I recently got the hang of loading PS2 backups from external USB hard drives, and have successfully done so with multiple games. Sadly, with any game from the Final Fantasy series this is not an option because USB 1.1 makes the cutscenes completely unwatchable and sometimes I feel like loading times increase instead of decrease.
Anyway, my latest experiment involves trying to get FFX International to install HDD data (a 1664 megabyte file which supposedly reduces loading times) on an unofficial external USB drive. The problem is that the system was designed to install on the official Sony HDD for the fat PS2, which isn't compatible with the slim PS2 (also the reason why you can't play online on the slim), so the option to Install to HDD in-game is greyed out for the moment.
My goal is to emulate the official Sony HDD and fat PS2 so that FFX International will allow me to install the data.
Okay, after some digging I discovered that all I need is the SonyPS2 HDD Utility Disc (preferably v1.10). And it looks like that's a dead end since I can't seem to find it anywhere. I have multiple torrents of it stuck at 80% with no seeders, dozens of 5 year old forum posts with dead links etc. etc.
I'll keep looking, but if anyone happens to have this baby just lying there, I'd really appreciate a link.