If you have no idea at all what you need, the best thing is to try to guess based on someone else's experience. Each individual client machine can average from less than 1 I/O per second (normal PC or Mac used for sales/accounting) to as much as 4 (fast workstation using large applications). A fast workstation running a compiler can happily average 3-4 MB/s in data transfer requests, and an imaging system can demand even more.
Our recommendation? Spy on someone with a similar configuration and try to estimate their bandwidth requirements from their bottlenecks and the volume of the screams from their users. We also recommend Brian Wong's
Configuration and Capacity Planning for Solaris Servers. While he uses Sun Solaris foremost in his examples, his bottlenecks are disks and network cards, which are common among all the major vendors. His tables for FTP servers also come very close to what we calculated for Samba servers, and make a good starting point.
