As data have been growing rapidly in data centers, deduplication storage systems continuously face challenges in providing the corresponding throughputs and capacities necessary to move backup data within backup and recovery window times. One approach is to build a cluster deduplication storage system with multiple deduplication storage system nodes. The goal is to achieve scalable throughput and capacity using extremely highthroughput (e.g. 1.5 GB/s) nodes, with a minimal loss of compression ratio. The key technical issue is to route data intelligently at an appropriate granularity. We present a cluster-based deduplication system that can deduplicate with high throughput, support deduplication ratios comparable to that of a single system, and maintain a low variation in the storage utilization of individual nodes. In experiments with dozens of nodes, we examine tradeoffs between stateless data routing approaches with low overhead and stateful approaches that have higher overhead but avoid imbalances that can adversely affect deduplication effectiveness for some datasets in large clusters. The stateless approach has been deployed in a two-node commercial system that achieves 3 GB/s for multi-stream deduplication throughput and currently scales to 5.6 PB of storage (assuming 20X total compression). 1

Data-protection class workloads, including backup and long-term retention of data, have seen a strong industry shift from tape-based platforms to disk-based systems. But the latter are traditionally designed to serve as primary storage and there has been little published analysis of the characteristics of backup workloads as they relate to the design of disk-based systems. In this paper, we present a comprehensive characterization of backup workloads by analyzing statistics and content metadata collected from a large set of EMC Data Domain backup systems in production use. This analysis is both broad (encompassing statistics from over 10,000 systems) and deep (using detailed metadata traces from several production systems storing almost 700TB of backup data). We compare these systems to a detailed study of Microsoft primary storage systems [22], showing that backup storage differs significantly from their primary storage workload in the amount of data churn and capacity requirements as well as the amount of redundancy within the data. These properties bring unique challenges and opportunities when designing a disk-based filesystem for backup workloads, which we explore in more detail using the metadata traces. In particular, the need to handle high churn while leveraging high data redundancy is considered by looking at deduplication unit size and caching efficiency. 1