Read other threads about ntfs with ps3 iso.
You must use prepNTFS, and i suggest you to use webman instead of multiman for mounting games. You can run ps3 and ps1 iso from ntfs usb hdd, but not ps3 games in folder format. Also ps2 classic, made to be used with ps2 classic launcher, must be in the internal hdd.
Ntfs hdd must be mbr and not gpt, thats important to know