面向分布式存储系统敏捷维护的同态自修复码
Homomorphic Self-repairing Codes for Agile Maintenance of Distributed Storage Systems
摘要：
分布式数据存储系统对于处理存储大量数据的需求至关重要。为了使这样的系统具有容错性，某种形式的冗余变得至关重要，这会产生各种开销-最突出的是存储空间和维护带宽要求。擦除码最初是为有损信道上的通信而设计的，它为基于复制的冗余提供了一种存储高效的替代方案，然而，当一些编码片段在一些存储设备故障后需要在新片段中补充时，它会带来用于维护的高通信开销。作为替代方案，我们提出了一个新的家庭的擦除码称为自修复码（SRC）考虑到分布式存储系统的特点，特别是维护过程。SRC具有以下显著特征：（a）通过下载比完整对象的大小更少的数据，可以直接从编码片段的其他子集修复编码片段，从而确保（b）从固定数量的编码片段修复片段，该数量仅取决于丢失了多少编码块并且与丢失了哪些特定块无关。本文通过定义新的自修复码奠定了基础，阐述了为什么定义的特性是分布式存储系统所需的。然后提出了同态自修复码（HSRC）作为一个具体的例子，其各个方面和性能的研究和比较-定量或定性相对于其他代码，包括传统的擦除码，以及其他最近的代码专门为存储应用程序。
英文摘要：
Distributed data storage systems are essential to deal with the need to store massive volumes of data. In order to make such a system fault-tolerant, some form of redundancy becomes crucial, incurring various overheads - most prominently in terms of storage space and maintenance bandwidth requirements. Erasure codes, originally designed for communication over lossy channels, provide a storage efficient alternative to replication based redundancy, however entailing high communication overhead for maintenance, when some of the encoded fragments need to be replenished in news ones after failure of some storage devices. We propose as an alternative a new family of erasure codes called self-repairing codes (SRC) taking into account the peculiarities of distributed storage systems, specifically the maintenance process. SRC has the following salient features: (a) encoded fragments can be repaired directly from other subsets of encoded fragments by downloading less data than the size of the complete object, ensuring that (b) a fragment is repaired from a fixed number of encoded fragments, the number depending only on how many encoded blocks are missing and independent of which specific blocks are missing. This paper lays the foundations by defining the novel self-repairing codes, elaborating why the defined characteristics are desirable for distributed storage systems. Then homomorphic self-repairing codes (HSRC) are proposed as a concrete instance, whose various aspects and properties are studied and compared - quantitatively or qualitatively with respect to other codes including traditional erasure codes as well as other recent codes designed specifically for storage applications.
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