When and by how much can helper node selection improve regenerating codes?

Regenerating codes (RCs) can significantly reduce the repair bandwidth of distributed storage networks. Initially, the analysis of RCs was based on the assumption that during the repair process, the newcomer does not distinguish (among all surviving nodes) which nodes to access, i.e., the newcomer is oblivious to the set of helpers being used. Such a scheme is termed the blind repair (BR) scheme. Nonetheless, it is intuitive in practice that the newcomer should access only those “good” helpers. This paper focuses on characterizing the effect of choosing the helper nodes in terms of the storage-bandwidth tradeoff. The results fully answer the following fundamental questions: Under what conditions does proactively choosing the helper nodes improve the storage-bandwidth tradeoff? Can this improvement be analytically quantified?