As computers become more capable, researchers of all types are finding it necessary to store massive quantities of data generated by simulations or experiments and to retrieve them at high rate for analysis or visualization. Strong needs have arisen for storage systems tuned for particular needs; significant improvements in storage speed and access control; optimized wide area network bulk transfers; utilization of new media and new types of storage devices; and development, testing, and use of user-written storage applications. The Oak Ridge National Laboratory (ORNL) and the National Energy Research Scientific Computing Center (NERSC) have formed a wide-area distributed testbed, entitled "Probe"-, to support challenging storage-related studies.