Increasing energy costs and the trend to green solutions are generating growing interest in eco-friendly computing. Flash storage technology satisfies low-energy requirements and falling prices for flash storage have recently made it possible to replace conventional hard disks with solid state drives. These can provide higher performance when deployed properly but they are still too expensive for the low-cost server market. In this paper we analyze inexpensive flash drives and conventional hard drives with a focus on energy efficiency. Our main goal is to decide whether replacing hard drives with USB flash drives is a reasonable and economic way to build energy-efficient servers. Our evaluation shows that despite the high throughput of hard disks, flash drives have a better performance per joule. In some cases, inexpensive USB flash can compete not only with hard disks but also with solid state drives.