Chapter 20 STORAGE RESOURCE MANAGERS Essential Components for the Grid

Storage Resource Managers (SRMs) are middleware components whose function is to provide dynamic space allocation and file management of shared storage components on the Grid. They complement Compute Resource Managers and Network Resource Managers in providing storage reservation and dynamic information on storage availability for the planning and execution of a Grid job. SRMs manage two types of resources: space and files. When managing space, SRMs negotiate space allocation with the requesting client, and/or assign default space quotas. When managing files, SRMs allocate space for files, invoke file transfer services to move files into the space, pin files for a certain lifetime, release files upon the clients request, and use file replacement policies to optimize the use of the shared space. SRMs can be designed to provide effective sharing of files, by monitoring the activity of shared files, and make dynamic decisions on which files to replace when space is needed. In addition, SRMs perform automatic garbage collection of unused files by removing selected files whose lifetime has expired when space is needed. In this chapter we discuss the design considerations for SRMs, their functionality, and their interfaces. We demonstrate the use of SRMs with several examples of real implementations that are in use today in a routine fashion or in a prototype form.