Conclusion

 What you can do to improve performance?

   You can ( in order of effectiveness)

• make sure the system has enough memory.
• correct problems of usage, caused by users and by the system.
• organize the system's hard disks and filesystems, maximizing I/O throughput.
• monitor your network not to be saturated with traffic and the error rate is low (netstat)
• configure the kernel to eliminate unwanted drivers and options, and use tables of an appropriate size.
• tune the filesystem's layout policies for individual disk.
• identify situations in which the system is fundamentally inadequate to satisfy the demands.