Research Fellow at CCS, University of Tsukuba. The author of NArray, a numerical library for Ruby. Pwrake aims at the high-performance parallel execution of data-intensive scientific workflows using multi-node clusters with >~10,000 cores. In the design of Pwrake, I made use of existing powerful tools. First, Pwrake is implemented as an extension to Rake. In this talk, I show that Rake is so power