Case studies in storage access by loosely coupled petascale applications

A large number of real-world scientific applications can be char-acterized as loosely coupled: the communication among tasks is infrequent and can be performed by using file operations. While these applications may be ported to large scale machines designed for tightly coupled, massively parallel jobs, direct implementations do not perform well because of the large number of small, latency-bound file accesses. This problem may be overcome through the use of a variety of custom, hand-coded strategies applied at various subsystems of modern near-petascale computers- but is a labor in-tensive process that will become increasingly difficult at the petas-cale and beyond. This work profiles the essential operations in the I/O workload for five loosely coupled scientific applications. We characterize the I/O workload induced by these applications and offer an analysis to motivate and aid the development of program-ming tools, I/O subsystems, and filesystems. 1