It's 10 gigabytes...12 Gigabytes for TetraMaster + PlayOnline + FFXI. A full install of FFXI on the PS2 still likely uses less 8GB once installed. Leaving 2GB for storing updates temporarily when they in the process of being downloaded. It's very likely that unexpected issue was caused by duplicate files that weren't properly removed after installations of updates. In any case this issue has been fixed.