Wiera: Policy-Driven Multi-Tiered Geo-Distributed Cloud Storage System

Multi-tiered geo-distributed cloud storage systems must tame complexity at many levels: uniform APIs for storage access, supporting flexible storage policies that meet a wide array of application metrics, determining an optimal data placement, handling uncertain network dynamics and access dynamism, and operating across many levels of heterogeneity both within and across data-centers (DCs). In this paper, we present an integrated solution called Wiera. Wiera enables the specification of data management policies both within a local DC and across DCs. Such policies enable the user to optimize for cost, performance, reliability, durability, and consistency, and to express their tradeoffs. In addition, Wiera determines an optimal data placement for the user to meet their desired tradeoffs easily in such an environment. A key aspect of Wiera is first-class support for dynamism due to network, workload, and access patterns changes. As far as we know, Wiera is the first geo-distributed cloud storage system which handles dynamism actively at run-time. Wiera allows unmodified applications to reap the benefits of flexible data/storage policies by externalizing the policy specification. We show how Wiera enables a rich specification of dynamic policies using a concise notation and describe the design and implementation of the system. We have implemented a Wiera prototype on multiple cloud environments, AWS and Azure, that illustrates potential benefits from managing dynamics and in using multiple cloud storage tiers both within and across DCs.