Getting maximum performance out of an OpenVPN setup can be difficult to achieve. On a clean Ethernet network, the default settings of OpenVPN are fairly good. However, some tuning is required on gigabit-speed networks.
When an ADSL or cable-modem connection is used, performance is also usually pretty good. However, under certain circumstances, the performance of our OpenVPN tunnel can fall way behind the performance of the normal network. These circumstances are almost always ISP-dependent, but nevertheless, it is worthwhile exploring how to increase performance.
The key to optimizing performance is to have good tools for measuring performance in the first place. Two basic, yet invaluable, tools for measuring network performance are
iperf tool is readily available on Linux, FreeBSD, and Mac OS. There are ports available for Windows and even Android.