Frugal storage for cloud file systems

Reviewer: David Bruce Henderson

Typical modern physical storage systems have a hierarchy of several tiers of storage, with data moving automatically between the various tiers depending on the frequency of access to the data. Fast but expensive storage is used for data that needs to be accessed quickly and frequently, while slower but less expensive storage is used for data that doesn't experience frequent access. The authors of this paper have developed a framework for applying this hierarchical storage strategy to cloud storage services. The authors present a short introduction to hierarchical storage, summarize related works, and then make their proposition. Basically, they contend that significant cost advantages can be achieved through a hierarchical structuring of multiple cloud storage offerings with different cost/performance characteristics. They present their frugal cloud file system (FCFS) as a solution and demonstrate its effectiveness using the pricing of Amazon's cloud service offerings. Cloud-based storage has a significant advantage over physical storage alternatives in that the size of the various tiers of storage can be dynamic rather than fixed. The proposed solution integrates multiple storage services and dynamically adapts the storage volume sizes of each service to improve cost effectiveness. The paper explains the solution at a high level, illustrated with graphs and figures. The authors then lay out their dynamic storage framework and two schemes for determining when and how to dynamically move data between the different storage tiers. The authors provide the results of simulations using real-life disk traces from a medium-sized data center to support their claims of cost effectiveness. The paper is supported by figures and associated cost examples that will be useful to those actively considering cloud storage as a strategic solution. A tiered hierarchical strategy for cloud storage seems intuitively to be a winner, just as hierarchical tiered physical storage was before it. All that is needed now is for someone to offer FCFS as a cloud service. Online Computing Reviews Service

Reviewer: Michael G. Murphy

As more and more enterprises look to cloud storage to meet their data storage needs at a lower cost of operation, this issue is of important practical significance. In this paper, Puttaswamy et al. address cost-effective cloud storage. They propose a frugal cloud file system (FCFS), a storage management application designed to reduce operating costs in the cloud. Specific comparisons are made to Amazon's Elastic Block Store (EBS), Simple Storage Service (S3), and ElastiCache, which represent of a variety of cloud storage options. The major tradeoff is between storage and access costs. Dynamically managing this tradeoff with products that emphasize one factor or the other offers significant overall cost savings. The first section provides a conceptual introduction, a summary of related work, and the authors' view of what this paper contributes to the field. Subsequent sections provide a motivating framework for dynamic storage; a careful description of FCFS; cost optimization algorithms, including cost analysis; experimental design and the nature of the real-life traces used; an evaluation of the results; and concluding thoughts. Twelve figures, three tables, and pseudocode for block reads in FCFS effectively complement the text. The paper is interesting and insightful within the constraints noted by the authors. It will be interesting to see whether significant contributions based on actual implementations are made to the literature on cloud storage, since such a report tends to become a postmortem after the technology moves forward and the older technology has lost its proprietary advantage. Online Computing Reviews Service