What do you consider a heavily traffficated DN site? 10, 20, even 90 current annonymous users? Our FanGap network receives over 50,000 users per day hitting the site generating hundreads of thousands of requests per day. Since the site is aimed at the tween set, our traffic balloons right after school hours.

Here's a sample of our traffic from peak times:

How do you keep a large DNN site responding when under a heavy load. The thing that is critical to high traffic applications is SQL. You really need to understand how SQL is impacting the IO on your SQL Server machine and make sure there are no bottlenecks. Granted there are many issues that can impact an application getting this kind of load, but you should start by making sure your SQL box is optimized at its fullest. We found in this case, that many of the bottlenecks we encountered early in the development process was IO issues on our SQL box. Here are some things to look out for.

• TempDB - Move the tempdb onto it's own drive if possible. We noticed some of the procedures on DNN making heavy use of the tempdb. Make sure you move it on to it's own drive. Also create more tempdbs. Usually about one per CPU in the machine. If it is a multicore CPU, then 1 per each core.
• Break Out the Logs and Data - This is a given, each requires its own kind of IO access. Break  them out.
• Memory - Load up on memory on the SQL box so it can cache and reduce the amount of disk IO.
• Keep an eye on it - Make sure you watch the SQL processes and see if there are an queries that are causing a bottleneck, It may require a better caching strategy on DNN.

Those are just a few items to look for. Make sure to check IO, memory, and CPU performance counters on both the web servers, and the SQL server to see where your bottleneck may be.