[fiddyschmitt]

Thanks J :) Absolutely! I did try various flags to optimise performance. For CreateFile (which in .NET is wrapped by the FileStream class) I tried FILE_WRITE_THROUGH (which is FileOptions.WriteThrough in .NET), and found it impacted performance quite a lot.

The key to high performance as you rightly pointed out was preventing flushing. In the end, what worked best was reducing the number of writes to disk (which is the bottleneck). I did that by buffering 10-50 ms worth of TCP data, coupled with only flushing explicitly (using a large buffer so that neither BinaryWriter or FileStream flush automatically).