  Contrary to the conclusions of a recent body of work where approximate
shortest remaining processing time first (SRPT) flow scheduling is advocated
for datacenter networks, this paper aims to demonstrate that per-flow fairness
remains a preferable objective. We evaluate abstract queuing models by analysis
and simulation to illustrate the non-optimality of SRPT under the reasonable
assumptions that datacenter flows occur in batches and bursts and not, as
usually assumed, individually at the instants of a Poisson process. Results for
these models have significant implications for the design of bandwidth sharing
strategies for datacenter networks. In particular, we propose a novel "virtual
fair scheduling" algorithm that enforces fairness between batches and is
arguably simple enough to be implemented in high speed devices.
