Coupling Right-Provisioned Cold Storage Data Centers with Deduplication

Modern cloud-scale cold storage data centers have begun to support right-provisioning of a rack’s resources (power, cooling, etc.), which allows only a small fraction of all hard disks to be active (spinning) concurrently at any given time to reduce the cost of ownership. Data deduplication is a traditional approach to split files into chunks and eliminate duplicate chunks, which can also cut costs for cold storage systems. However, when combined with right-provisioning, classical deduplication may make a file deduplicated and stored across the disks some of which are not active currently, thus leading to unacceptable access performance caused by spinning up and down of the disks. In this paper, we analyze the deduplication ratio under real-world workloads of cloud cold storage and observe for most workloads: 1) the deduplication ratio generally increases quickly with the first few of versions of the workload, and 2) increases slowly but steadily with the subsequent versions as a long tail. Based on the first observation, we propose an online deduplication way that can improve the deduplication ratio while providing acceptable read performance; based on the second one, we propose an additional offline deduplication way that can achieve comparable deduplication ratios with classical deduplication. We design a cold storage system called DeCold via combining the above two deduplication ways as well as improving deduplication efficiency. We prototype DeCold and conduct testbed experiments on real-world datasets including source code, virtual machine and database. Evaluations show that DeCold achieves better file access performance over the classical deduplication implementation, while maintaining decent deduplication efficiency.