Nowadays, storing and retrieving information over the Cloud is critical for the survival and growth of organizations and people. In this context, the possibility to store a huge amount of data and files on remote third-party Cloud storage providers is becoming an even more concrete practice. Unfortunately, there is not any guarantee regarding data availability and reliability of such providers. In such a context, if the Cloud wants to use the storage as a service of another Cloud, it has only to trust it. A possible solution consists of using a Multi-Cloud Storage (MCS) system. However, how organizations should compose their own MCS system on geo-distribution basis is not trivial at all. In this paper, we specifically discuss how to optimize the overall system in terms of data storage and retrieval by testing and validating a MCS system composed of three major Cloud Storage providers; Dropbox, Google Drive and Copy …