This paper presents the design of G-IDSS (Graph-based InnoCyPES Data Storage Service): a novel, distributed data storage service that is built around a P2P network overlay to support handling distributed data. G-IDSS is accessible through a standard command-line interface and is based on a graph database to support the schema-less management of the distributed data stored among peers. The mechanisms to facilitate the execution of complex queries requiring distributed data integration and fusion are also presented and discussed. Besides the design, this work also provides relevant details related to the implementation of G-IDSS, reflecting several use cases that demand data that are distributed across different, even geographically spread, locations. G-IDSS scales to thousands of peers in an overlay, it is able to run distributed queries and can integrate data that are stored in different sources.