DR-Update: A Dual-Level Relay Scheme in Erasure-Coded Storage Systems for Balanced Updates
Mingzhu Deng, Songping Yu, Nong Xiao, Fang Cherry Liu, Zhiguang Chen · 2017
The conventional update scheme of erasure-coded systems adopts a naive star structure for data transmission, causing excessive cross-rack traffic and suffering from potential single-node bottleneck problem, which, if not addressed, would throttle the system before any repair process optimization takes effect. In this paper, we propose DR-Update: A Dual-level Relay Update scheme to 1) minimize cross-rack traffic, 2) alleviate the single-node bottleneck problem, and 3) further balance rack-level update traffic and node-level connections. Specifically, DR-Update minimizes cross-rack traffic by introducing a rack set and intra-rack relay, and further mitigates the single-node bottleneck problem of the starting node by enabling cross-rack relay. To achieve both rack-level and node-level balance, a balanced linear transmission structure is constructed with respect to both the outbound degree of each involved node and update traffic across related rack. Furthermore, extensive trace-driven experiment results show that DR-Update not only manages to reduce excessive cross-rack traffic but also maintains balance of the system on both node level and rack level. For example, a roughly 16% average cross-rack traffic can be saved by DR-Update across all ten traces and both node-level and rack-level balance are achieved.