To answer this question, you need to understand the factors that can improve performance in web and FTP servers.
Option A) Minimize FTP user isolation - This option is incorrect. Minimizing FTP user isolation can improve performance by reducing the overhead of managing multiple user accounts and permissions.
Option B) Use ISAPI extensions instead of ISAPI filters - This option is incorrect. Using ISAPI extensions instead of ISAPI filters can improve performance by reducing the processing overhead for each request.
Option C) Set up remote virtual directories - This option is correct. Setting up remote virtual directories can negatively impact performance. Accessing files from remote locations can introduce latency and increase the time it takes to serve requests.
Option D) Keep websites and FTP servers on different machines - This option is incorrect. Keeping websites and FTP servers on different machines can improve performance by distributing the load across multiple servers.
The correct answer is C. Setting up remote virtual directories is not a good trick for improving performance because it can introduce latency and increase the time it takes to serve requests.