Repair for Distributed Storage Systems in Packet Erasure Networks
  Reliability is essential for storing files in many applications of distributed storage systems. To maintain reliability, when a storage node fails, a new node should be regenerated by a repair process. Most of the previous results on the repair problem assume perfect (error-free) links in the networks. However, in practice, especially in a wireless network, the transmitted packets (for repair) may be lost due to, e.g., link failure or buffer overflow. We study the repair problem of distributed storage systems in packet erasure networks, where a packet loss is modeled as an erasure. The minimum repair-bandwidth, namely the amount of information sent from the surviving nodes to the new node, is established under the ideal assumption of infinite number of packet transmissions. We also study the bandwidth-storage tradeoffs in erasure networks. Then, the use of repairing storage nodes (nodes with smaller storage space) is proposed to reduce the repair-bandwidth. We study the minimal storage of repairing storage nodes. For the case of a finite number of packet transmissions, the probability of successful repairing is investigated. We show that the repair with a finite number of packet transmissions may use much larger bandwidth than the minimum repair-bandwidth. Finally, we propose a combinatorial optimization problem, which results in the optimal repair-bandwidth for the given packet erasure probability and finite packet transmissions. 
Majid Gerami, Ming Xiao, Jun Li, Carlo Fischione, Zihuai Lin
cs.IT math.IT