StoRM: A flexible solution for Storage Resource Manager in grid

In these times, scientific data intensive applications generate ever-increasing volumes of data that need to be stored, managed, and shared between geographically distributed communities. Data centres are normally able to provide tens of petabytes of storage space through a large variety of heterogeneous storage and file systems. However, storage systems shared by applications need a common data access mechanism, which allocates storage space dynamically, manages stored content, and automatically remove unused data to avoid clogging data stores. To accommodate these needs, the concept of Storage Resource Managers (SRMs) was devised in the context of a project that involved High Energy Physics (HEP) and Nuclear Physics (NP). The Storage Resource Manager (SRM) interface specification was defined and evolved into an international collaboration in the context of the Open Grid Forum (OGF). SRM interface provides the technology needed to share geographically distributed heterogeneous storage resources, with an effective and common interface regardless of the type of the back-end system being used. By implementing the SRM interface, grid storage services provide a consistent homogeneous interface to the Grid to manage storage resource as well as advanced functionality such as dynamic space allocation and file management on shared storage systems. Within Worldwide LHC Grid project exists more than five interoperating implementations of SRM services, and every one shows peculiarity. In this paper, we describe the flexibility of StoRM service, an implementation of the Storage Resource Manager Interface version 2.2. StoRM is designed to foster the adoption of cluster file systems, and thanks to the marked flexibility, StoRM can be used in small data centre with human resource deficiency to administer an other grid service and, at the same time, capable to grow in terms of storage managed and workload. StoRM can be used to manage any storage resources with any kind of POSIX file-system in a transparent way. As demonstration of the StoRM flexibility, the paper describes how applications scheduled via Grid can access files on a file-system directly via POSIX calls, how StoRM can be deployed in a clustered configuration to address scalability needs and finally how StoRM can be used to manage also storage classes based on Storage Cloud, like Amazon Simple Storage Service (S3).