Abstract Even though their capacities are still orders of mag- nitude lower than those of hard disks, flash storage sys- tems are rapidly gaining importance in energy-constrained systems. This paper focuses on USB flash drives, which can provide portable storage to mobile systems or stor- age to systems that otherwise do not have persistent stor- age opportunities (e.g., low-power sensor devices). The paper presents studies relating to power consumption, en- ergy overheads and benefits, and performance impacts of USB flash drives. The key insights obtained from these ex- periments are that (i) read/write costs are not significantly greater than idle costs and (ii) the size of the flash itself has only limited bearing on energy consumption.
Kyle Oâ„¢Brien, David C. Salyers, Aaron D. Striegel, Christian Poellabauer
Department of Computer Science and Engineering
University of Notre Dame
Notre Dame, IN 46556 USA
Storage components of mobile wireless systems, including laptops, handhelds, and sensor devices, are essential for temporary and long-term preservation of information. In the recent past, solid state, or flash storage, has emerged as a promising alternative to hard disks. While flash memory and drives offer the potential for very low-power storage, they are still significantly smaller than available disk drives . USB flash drives provide an opportunity to extend an existing mobile/wireless device with (additional) storage capacity; this is particularly important for small low-power devices that otherwise do not have any storage opportunities (e.g., TelosB motes and Crossbow Stargate wireless mesh routers). With newer areas of research such as Delay Tolerant Networking (DTN) , on-device flash capacities are often not enough. Finally, in the absence of designing a new device solely for their research, researchers are often faced with employing USB flash drives to meet that need. Unfortunately, the performance of said devices with regards to energy and read/write speeds is poorly understood. The usage of flash for the network researcher is especially critical as the choice of flash can have a profound effect on the energy and performance characteristics of the overarching system or application. Toward this end, this paper provides a comprehensive assessment of the power, energy, and performance characteristics of flash drives. Specifically, the contributions of this work can be summarized as follows: Â¢ Comprehensive study of USB flash drive power con- sumption: This paper experimentally examines the power consumption characteristics of USB flash drives across a wide variety of considerations including manufacturer, device size, operating system, read/write blocks, and USB connection types (1.1 or 2.0). Â¢ Comprehensive performance studies: Further, this paper evaluates the energy - performance tradeoff of USB flash drives, assessing the energy costs and performance numbers of various I/O accesses to a USB flash storage.