Do not cascade hubs beyond four levels on either SPARC based systems or x86 based systems. On SPARC systems, the OpenBoot PROM cannot reliably probe beyond four levels of devices.
Do not plug a bus-powered hub into another bus-powered hub in a cascading style. A bus-powered hub does not have its own power supply.
Do not connect a device that requires a large amount of power to a bus-powered hub. These devices might be denied connection to bus-powered hubs or might drain the hub of power for other devices. An example of such a device is a USB diskette device.