Do not cascade hubs beyond four levels on either SPARC based or IA based systems. On SPARC systems, the OpenBootTM PROM cannot reliably probe beyond four levels of devices.
Do not cascade bus-powered hubs. So, you cannot plug a bus-powered hub into another bus-powered hub. A bus-powered hub does not have its own power supply. A USB diskette device derives all its power from the bus and might not work on a bus-powered hub.