XHR-Code: An Efficient Wide Stripe Erasure Code to Reduce Cross-Rack Overhead in Cloud Storage Systems

Nowadays wide stripe erasure codes (ECs) become popular as they can achieve low monetary cost and provide high reliability for cold data. Generally, wide stripe erasure codes can be generated by extending traditional erasure codes with a large stripe size, or designing new codes. However, although wide stripe erasure codes can decrease the storage cost significantly, the construction of lost data is extraordinary slow, which stems primarily from high cross-rack overhead. It is because a large number of racks participate in the construction of the lost data, which results in high cross-rack traffic. To address the above problems, we propose a novel erasure code called XOR-Hitchhiker-RS (XHR) code, to decrease the cross-rack overhead and still maintain low storage cost. The key idea of XHR is that it utilizes a triple dimensional framework to place more chunks within racks and reduce global repair triggers. To demonstrate the effectiveness of XHR-Code, we provide mathematical analysis and conduct comprehensive experiments. The results show that, compared to the state-of-the-art solutions such as ECWide under various failure conditions, XHR can effectively reduce cross-rack repair traffic and the repair time by up to 36.50%.