A Fundamental Trade-Off between the Download Cost and Repair Bandwidth in Distributed Storage Systems

Abstract

Distributed storage systems are mainly justified due to the limited amount of storage capacity and improving the reliability through distributing data over multiple storage nodes. However, it may happen the data is stored in unreliable nodes, while it is desirable the end user to have a reliable access to the stored data. So,~in an event that a node is damaged,~to prevent the system reliability to regress,~it is necessary to regenerate a new node with the same amount of stored data as the damaged node to retain the number of storage nodes, thereby having the previous reliability. This requires the new node to connect to some of existing nodes, and downloads the required information, thereby occupying some bandwidth, called the repair bandwidth. On the other hand, it is more likely the cost of downloading varies across different nodes. This paper aims at investigating the fundamental trade-off between the download cost and repair bandwidth, and more importantly, it is shown any point on this curve can be achieved through the use of the so called generalized regenerating codes which is an enhancement to the regenerating codes introduced by Dimakis et al. in~\cite{dim1}.