Assuming the information I’ve seen in a couple of places online regarding the 2TB per-device limit and 1TB internal drive limit are accurate, the theoretical limit is 505 TB, achieved by upgrading the internal drive to 1TB and connecting 126 2TB storage devices to each of the two USB ports. This limit is a function of limitations inherent in USB itself, which allows only 127 devices to be connected to a single host controller (and each hub counts as one of those 127 devices).
Actually achieving that requires that:
- The external USB ports are on independent host controllers and the internal Bluetooth controller is not connected via USB. I’ve not been able to find any conclusive information about this, but it’s statistically unlikely for USB 2.0 ports, as almost all platforms use internal hubs. If that is the case, you’re limited to 126 external devices, or 125 if Bluetooth is connected internally via USB.
- You can actually find a 126 port USB hub. These simply do not exist, at least not as single devices from a USB perspective. Essentially nobody makes a chip that’s more than a four port hub (7 port hubs involve one of these connected to one of the ports of another, higher port counts use similar daisy-chaining). Factoring in a proper balanced tree, you need 22 hubs on each port, which cuts the number of usable external devices to 105/104 (if the ports are on one controller) or 210/208 (if the ports are on separate controllers).
So if we factor in practical hardware limitations, there’s a functional upper bound of 209 TB (assuming regular four-port hubs externally, one internal hub used for the two external ports, and Bluetooth eating one of the device addresses).
In reality, such a setup is unlikely to work very reliably for a number of reasons though, and it’s entirely likely that the PS3’s USB controllers can’t actually handle that many devices (which would further lower that limit).