Checking the Data Cloud Consistency by Auditor Method

Cloud storage services can be regarded as a typical service in the cloud computing, which involves the delivery of the data storage including database like services and network attached storage. And the cloud storage services have become very popular due to their huge advantages. To provide everywhere always-on access, a cloud service provider (CSP) maintains multiple replicas for each piece of data on geographically distributed servers. A key problem of using the replication technique in clouds is that it is very expensive to achieve strong consistency on a worldwide scale. In this paper, we present a new consistency as a service (CaaS) model, which consists of a large data clouds and multiple small audit clouds. In the CaaS model, a data cloud is maintained by a CSP, and a group of users that constitute an audit cloud can verify whether the data cloud provides the promised level of consistency or not. We also proposed two-level auditing architecture, which only requires a loosely synchronized clock in the audit cloud. Then, it designed algorithms to quantify the severity of violations with two metrics the commonality of violations, and the staleness of the value of a read. Finally, it devise a heuristic auditing strategy (HAS) to reveal as many violations as possible. Extensive experiments were performed using a combination of simulations and a real cloud deployment to validate HAS.