The Disk
There is a number of SRM implementations in use, with varying capabilities. The Disk Pool Manager (DPM) is used for fairly small SEs with disk-based storage only, while CASTOR is designed to manage large-scale MSS, with front-end disks and back-end tape storage. dCache is targeted at both MSS and large-scale disk array storage systems. Other SRM implementations are in development, and the SRM protocol specification itself is also evolving.