The performance of distributed storage systems deployed on wide-area networks can be improved using weighted (majority) quorum systems instead of their regular variants due to the heterogeneous performance of the nodes. A significant limitation of weighted majority quorum systems lies in their dependence on static weights, which are inappropriate for systems subject to the dynamic nature of networked environments. To overcome this limitation, such quorum systems require mechanisms for reassigning weights over time according to the performance variations. We study the problem of node weight reassignment in asynchronous systems with a static set of servers and static fault threshold. We prove that solving such a problem is as hard as solving consensus, i.e., it cannot be implemented in asynchronous failure-prone distributed systems. This result is somewhat counter-intuitive, given the recent results showing that two related problems -- replica set reconfiguration and asset transfer -- can be solved in asynchronous systems. Inspired by these problems, we present two versions of the problem that contain restrictions on the weights of servers and the way they are reassigned. We propose a protocol to implement one of the restricted problems in asynchronous systems. As a case study, we construct a dynamic-weighted atomic storage based on such a protocol. We also discuss the relationship between weight reassignment and asset transfer problems and compare our dynamic-weighted atomic storage with reconfigurable atomic storage.

翻译：部署在广域网上的分布式存储系统，由于节点性能的异质性，使用加权（多数）法定人数系统代替常规变体可提升性能。加权多数法定人数系统的一个显著局限性在于其依赖静态权重，而这并不适用于网络环境动态变化的系统。为克服此局限，此类法定人数系统需要根据性能变化随时间重新分配权重的机制。我们研究了在服务器集静态且故障阈值静态的异步系统中节点权重重新分配的问题。我们证明解决该问题与解决共识问题同样困难，即无法在异步易故障分布式系统中实现。这一结果有些反直觉，因为近期研究表明两个相关问题——副本集重配置和资产转移——可在异步系统中解决。受这些问题启发，我们提出了两个包含服务器权重及其重新分配方式约束的问题版本。我们设计了一个协议，用于在异步系统中实现其中一个受限问题。作为案例研究，我们基于该协议构建了动态加权原子存储。我们还讨论了权重重新分配与资产转移问题之间的关系，并将我们的动态加权原子存储与可重构原子存储进行了比较。