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In the gLite grid model a site will typically have a Storage Element (SE) that has no direct mechanism for updating any central or experiment-specific catalogues. This loose coupling was a deliberate decision that simplifies SE design; however, a consequence of this is that the catalogues may provide an incorrect view of what is stored on a SE. In this paper, we present SynCat: a mechanism to allow catalogues to re-synchronise with SEs. The paper describes how catalogues can be sure, within certain tolerance, that files believed to be stored at various SEs are really stored there. SynCat also allows catalogues to be aware of transitory file metadata (such as whether a file normally stored on tape is currently available from disk) with low latency.

Storage Services are crucial components of the Worldwide LHC Computing Grid Infrastructure spanning more than 200 sites and serving computing and storage resources to the High Energy Physics LHC communities. Up to tens of Petabytes of data are collected every year by the four LHC experiments at CERN. To process these large data volumes it is important to establish a protocol and a very efficient interface to the various storage solutions adopted by the WLCG sites. In this work we report on the experience acquired during the definition of the Storage Resource Manager v2.2 protocol. In particular, we focus on the study performed to enhance the interface and make it suitable for use by the WLCG communities. At the moment 5 different storage solutions implement the SRM v2.2 interface: BeStMan (LBNL), CASTOR (CERN and RAL), dCache (DESY and FNAL), DPM (CERN), and StoRM (INFN and ICTP). After a detailed inside review of the protocol, various test suites have been written identifying the most effective set of tests: the S2 test suite from CERN and the SRM- Tester test suite from LBNL. Such test suites have helped verifying the consistency and coherence of the proposed protocol and validating existing implementations. We conclude our work describing the results achieved.