No abstract

Many Cloud applications exploit the diversity of storage options in a data center to achieve desired cost, performance, and durability tradeoffs. It is common to see applications using a combination of memory, local disk, and archival storage tiers within a single data center to meet their needs. For example, hot data can be kept in memory using ElastiCache, and colder data in cheaper, slower storage such as S3, using Amazon as an example. For user-facing applications, a recent trend is to exploit multiple data centers for data placement to enable better latency of access from users to their data. The conventional wisdom is that co-location of computation and storage within the same data center is a key to application performance, so that applications running within a data center are often still limited to access local data. In this paper, using experiments on Amazon, Microsoft, and Google clouds, we show that this assumption is false, and that accessing data in nearby data centers may be faster than local access at different or even same points in the storage hierarchy. This can lead to not only better performance, but also reduced cost, simpler consistency policies and reconsidering data locality in multiple DCs environment. This argues for an expansion of cloud storage tiers to consider non-local storage options, and has interesting implications for the design of a distributed storage system.

No abstract

Cloud providers offer an array of storage services that represent different points along the performance, cost, and durability spectrum. If an application desires the composite benefits of multiple storage tiers, then it must manage the complexity of different interfaces to these storage services and their diverse policies. We believe that it is possible to provide the benefits of customized tiered cloud storage to applications without compromising simplicity using a lightweight middleware. In this paper, we introduce Tiera, a middleware that enables the provision of multi-tiered cloud storage instances that are easy to specify, flexible, and enable a rich array of storage policies and desired metrics to be realized. Tiera's novelty lies in the first-class support for encapsulated tiered cloud storage, ease of programmability of data management policies, and support for runtime replacement and addition of policies and tiers. Tiera enables an application to realize a desired metric (e.g., low latency or low cost) by selecting different storage services that constitute a Tiera instance, and easily specifying a policy, using event and response pairs, to manage the life cycle of data stored in the instance. We illustrate the benefits of Tiera through a prototype implemented on the Amazon cloud. By deploying unmodified MySQL database engine and a TPC-W Web bookstore application on Tiera, we are able to improve their respective throughputs by 47% − 125% and 46% − 69%, over standard deployments. We further show the flexibility of Tiera in achieving different desired application metrics with minimal overhead.