Proportional Service Allocation in Distributed Storage Systems

Fully distributed storage systems have gained popularity in the past few years because of their ability to use cheap commodity hardware and their high scalability. While there are a number of algorithms for providing differentiated quality of service to clients of a centralized storage system, the problem has not been solved for distributed storage systems. Providing performance guarantees in distributed storage systems is more complex because clients may have different data layouts and access their data through different coordinators (access nodes), yet the performance guarantees required are global. This paper presents a distributed scheduling framework. It is an adaptation of fair queuing algorithms for distributed servers. Specifically, upon scheduling each request, it enforces an extra delay (possibly zero) that corresponds to the amount of service the client gets on other servers. Different performance guarantees, e.g., per storage node proportional sharing, total service proportional sharing or mixed, can be met by different delay functions. The delay functions can be calculated at coordinators locally so excess communication is avoided. The analysis and experimental results show that these new algorithms can enforce performance goals under different data layouts and workloads.