Reducing Repair Traffic with Exact and Uncoded Repair in Distributed Storage Systems: Intersecting Zigzag Sets Codes on Hierarchical Codes

Erasure code is an efficient redundancy solution to avoid permanent data losses in distributed storage system. By using erasure code, the original data is encoded into blocks which are stored on different nodes. When one node fails, the lost data block needs to be recovered by transmitting a large number of data from helper nodes, which is called repair. Intersecting zigzag sets codes (IZS codes) and hierarchical code are two kinds of codes which reduce the bandwidth overhead in repair. IZS codes reduce the amount of data uploaded by each helper node, while hierarchical codes reduce the number of nodes participating in repair. In this paper, we propose a class of code called intersecting zigzag sets-hierarchical code (IZ2SHC code) to unify them together. IZ2SHC code decreases repair degree as hierarchical code and reduces repair overhead compared with the latter. Besides, it realizes exact regeneration of the failed data, and need not encode in helper node during the repair, which reduces disk read cost for helper node when transferring data in repair.