Distributed storage systems from combinatorial designs

Large scale distributed storage systems are used in several contexts, such as social networking sites (Facebook, Google+ etc.) and cloud storage (Amazon, Microsoft etc.). Regenerating codes allow for reliable data access in these systems even in the presence of individually unreliable nodes, while striving for a node repair mechanism that consumes as few resources (e.g., downloaded packets, nodes accessed) as possible. In this talk, I will discuss our recent work on constructing regenerating codes from combinatorial designs. Combinatorial design theory has its roots in recreational mathematics and is concerned with the arrangement of the elements of a finite set into subsets, such that the collection of subsets has certain "nice" properties. I will discuss our code constructions that are derived from Steiner systems, affine geometries, Hadamard designs, mutually orthogonal Latin squares and high-girth graphs. Our codes allow for failure recovery by simply downloading packets from the surviving nodes and allow for the repair degree (i.e., the number of nodes contacted for node repair) to be varied in a simple manner. Determining the code rate of these constructions is challenging and prior work has primarily provided lower bounds on the rate. For most of our constructions we are able to determine the code rate for a range of code parameters.
Aditya Ramamoorthy is an Associate Professor at Iowa State University. He received his B. Tech. from the Indian Institute of Technology, Delhi and the M.S. and Ph.D. degrees from the University of California, Los Angeles (UCLA). His research interests are in the areas of network information theory, channel coding and signal processing for nanotechnology and bioinformatics. Dr. Ramamoorthy serves as an associate editor for the IEEE Transactions on Communications. He is the recipient of the 2012 Iowa State University's Early Career Engineering Faculty Research Award, the 2012 NSF CAREER award, and the Harpole-Pentair professorship in 2009 and 2010.