Active Disks: Remote Execution for Network-Attached Storage (CMU-CS-97-198)

The principal trend in the design of computer systems is the expectation of much greater computational power in future generations of microprocessors. This trend applies to embedded systems as well as host processors. As a result, devices such as storage controllers have excess capacity and growing computational capabilities. Storage system designers are exploiting this trend with higher-level interfaces to storage and increased intelligence inside storage devices. One development in this direction is Network-Attached Secure Disks (NASD) which attaches storage devices directly to the network and raises the storage interface above the simple (fixed-size block) memory abstraction of SCSI. This allows devices more freedom to provide efficient operations; promises more scalable subsystems by offloading file system and storage management functionality from dedicated servers; and reduces latency by executing common case requests directly at storage devices. In this paper, we push this increasing computation trend one step further. We argue that application-specific code can be executed at storage devices to make more effective use of device, host and interconnect resources and significantly improve application I/O performance. Remote execution of code directly at storage devices allows filter operations to be performed close to the data; enables support of timing-sensitive transfers and application-aware scheduling of access and transfer; allows management functions to be customized without requiring firmware changes; and makes possible more complex or specialized operations than a general-purpose storage interface would normally support. This research is sponsored by DARPA/ITO through ARPA Order D306, and issued by Indian Head Division, NSWC under contract N00174-96-0002. The project team is indebted to generous contributions from the member companies of the Parallel Data Consortium. At the time of this writing, these companies include Hewlett-Packard Laboratories, Symbios Logic Inc., Compaq Corporation, Data General, Quantum Corporation, Seagate Technology, and Storage Technology Corporation. The views and conclusions contained in this document are those of the authors and should not be interpreted as representing the official policies, either expressed or implied, of any supporting organization or the U. S. Government. 1 Department of Electrical and Computer Engineering, Carnegie Mellon University