schemes. In the Part II paper, an explicit construction of an exact-repair code is proposed that achieves the minimum-bandwidth-regenerating (MBR) point of the FHS scheme. The new exact-repair code can be viewed as a generalization of the existing *fractional repetition* code.
bibliography:
- 'paper.bib'
title: 'When Can Helper Node Selection Improve Regenerating Codes? Part I: Graph-Based Analysis'
---

Distributed storage, regenerating codes, family helper selection schemes, helper nodes, fractional repetition codes, network coding

Introduction {#sec:intro}
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need for storing very large amounts of data reliably is one of the major reasons that has pushed for distributed storage systems. Examples of distributed storage systems include data centers [@ghemawat2003google] and peer-to-peer systems [@rhea2001maintenance; @bhagwan2004total]. One way to protect against data loss is by replication coding, i.e, if a disk in the network fails, it can be replaced and its data can be recovered from a replica disk. Another way is to use maximum distance separable (MDS) codes. Recently, regenerating codes (RCs) [@dimakis2010network] have been proposed to further reduce the repair-bandwidth of MDS codes.

One possible mode of operation is to let the *newcomer*, the node that replaces the failed node, [*always*]{} access/connect to all the remaining nodes. On the other hand, under 