A lot of the 'heat' being generated here appears to stem from the absence
of a good definition for "scalability" in the article. This is a common
Scalability is an abstact notion. So are terms like "reliability", and the
word "performance" itself. One person's meat is another's poison. With
regard to computer system performance, you might desire to optimize such
metrics as, throughput, response time, or resource utilization; to name a
few. The goal depends on the context. If you're printing reports at the end
of the financial year, MAXIMUM throughput is likely to be your goal. In
contrast, many web applications focus on MINIMIZING user response time.
Simply put, 'scalability' is a relation among variables (performance
metrics) that characterizes the rate of diminishing returns as the
dimensions of the system are increased. This means that scalability can
actually be expressed in a mathematical form. I've tried to illuminate this
point elsewhere http://www.perfdynamics.com/papers.html. Specifially,
http://xxx.lanl.gov/abs/cs.DC/0210017 should be of interest.