Designing server clusters for intermittent power introduces new possibilities to make them cheaper, greener, and more reliable, including leveraging variable electricity prices to buy more power when it is cheap, increasing the use of clean renewable energy, and capping power at low levels to extend UPS lifetime during blackouts. However, regulating power usage to take advantage of these possibilities is challenging, since applications often access persistent distributed state, where power fluctuations impact I/O performance and data availability. To address the problem, we design and implement BlinkFS, which combines a blinking abstraction with a power-balanced data layout and popularity-based replication/reclamation to optimize I/O throughput and latency as power varies. Our experiments show that BlinkFS outperforms existing approaches, particularly at low steady power levels and high levels of intermittency. As one example of our results, we show that BlinkFS reduces completion time for MapReduce-style jobs by 42% at 50% full power compared to an existing energy-proportional DFS.