Note: PS2 USB ports are USB 1.1, which causes slow loading times and potential stuttering in video cutscenes. If you'd like, I can:
Use Free DVD Boot (burned to a DVD-R) or a pre-modded memory card to launch the FMCB Installer through uLaunchELF . Mcboot Download Usb
Create a folder named DVD on your USB drive and place your ISO games there. Note: PS2 USB ports are USB 1
For formatting USB drives larger than 32GB to FAT32. General Installation Steps: Mcboot Download Usb
If your games are larger than 4GB, you must use USBUtil to split them.