T. Perelmutov (FERMI NATIONAL ACCELERATOR LABORATORY)
Storage Resource Managers (SRMs) are middleware components whose function is to provide dynamic space allocation and file management on shared storage components on the Grid. SRMs support protocol negotiation and reliable replication mechanism. The SRM standard allows independent institutions to implement their own SRMs, thus allowing for a uniform access to heterogeneous storage elements. SRMs leave the policy decision to be made independently by each implementation at each site. Resource Reservations made through SRMs have limited lifetimes and allow for automatic collection of unused resources thus preventing clogging of storage systems with "forgotten" files. The storage systems can be classified on basis of their longevity and persistence of their data. Data can also be temporary or permanent. To support these notions, SRM defines Volatile, Durable and Permanent types of files and spaces. Volatile files can be removed by the system to make space for new files upon the expiration of their lifetimes. Permanent files are expected to exist in the storage system for the lifetime of the storage system. Finally Durable files have both the lifetime associated with them and a mechanism of notification of owners and administrators of lifetime expiration, but cannot be deleted automatically by the system and require explicit removal. Fermilab's data handling system uses the SRM management interface, the dCache Distributed Disk Cache and the Enstore Tape Storage System as key components to satisfy current and future user requests. Storage Resource Manager specification is a result of international collaborative effort by representatives of JLAB, LBNL, FNAL, EDG-WP2 and EDG-WP5.