FireWire capable Macintosh computers support a maximum of 63 powered FireWire devices. You can connect a maximum of 16 FireWire devices in one chain.
Bus-powered FireWire Devices
When connecting multiple bus-powered FireWire devices to a computer, be careful that the total power consumed by the devices isn't more than the computer can provide. If the power draw exceeds the computer's limit, all devices on the FireWire bus may shut down unexpectedly during heavy activity. For example, copying several files from one FireWire drive to another.
If you experience FireWire devices shutting down unexpectedly: