Haechi: A Token-based QoS Mechanism for One-sided I/Os in RDMA based Storage System

Abstract

Advances in persistent memory and networking hardware are changing the architecture of storage systems and data management services in datacenters. Distributed, one-sided RDMA access to memory-resident data shows tremendous improvements in throughput, latency and server CPU utilization of storage servers. However, the silent nature of one-sided I/O simultaneously creates new challenging problems for providing QoS in such systems. In this paper, we propose Haechi, a work-conserving, token-based QoS mechanism to guarantee reservations and limits in storage systems that provide one-sided I/O services. Haechi decouples QoS enforcement into a QoS engine at the client and a QoS monitor at the data node. It leverages adaptive token dispatch, token conversion, and silent I/O reporting to guarantee the reservations of distributed clients while maintaining high server utilization. Empirical evaluations on the Chameleon cluster, with different reservation distributions and I/O access patterns, show that Haechi is successful in providing differentiated QoS with negligible overhead for token management.