Data transfer speed to USB storage connected to wifi router very slow
If you're talking about 3 Megabytes/second and have connected your MBP via Wifi, not ethernet cable, that speed is ok.
There are 3 limitations here:
- the WiFi - even at 802.11n it's hard to get more than 8 Mbyte/s throughput under very good conditions
- the smb protocol is quite inefficient, especially with latencies induced by a wireless connection.
- most routers are not very powerful, so they hardly manage more than 10Mbyte/s to USB drives anyway.
Try connecting to the router via cable, that should speed things up considerably.