We frequently need to transfer huge files (upwards of 50 GB) between two hosts, and the transfer rate never seems to reach the expected throughput for the network. There are several points which could be the bottleneck, but each of their theorical upper limit are way over the actual transfer rate. Here's a typical setup :
Laptop --> 802.11n --> AP --> CAT 6 cable --> 10/100 Mbits router --> Desktop
In this connection, the bottleneck is clearly the router, which would limit the transfer rate at 100 Mbits/sec. Even then, I rarely see a transfer rate (with scp) exceeding 9.5 MB/s, which represents 76 Mbits/sec, or only 76% of theorical maximum limit.
Can there really be a 24% overhead at the access point, or is there something else limiting the speed? It could be disk I/O (although SATA is rated at 1.5 Gbps), or anything on the motherboard between the disk and the NIC (how can I measure that?).
Is there a way to know for sure(*) where the bottleneck is? If I can't get more than 76 Mbps from a 100 Mbps router, will upgrading the network to gigabit increase throughput or will I still get 76 Mbps because the bottleneck is elsewhere?
(*) or at least in a way convincing enough that a boss would agree to invest to upgrade that one part of the network