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We present Nswap2L, a fast backing storage system for general purpose clusters. Nswap2L implements a single device interface on top of multiple heterogeneous physical storage devices, particularly targeting fast random access devices such as Network RAM and flash SSDs. A key design feature of Nswap2L is the separation of the interface from the underlying physical storage, data that are read and written to our ``device" are managed by our underlying system and may be stored in local RAM, remote RAM, flash, local disk or any other cluster-wide storage. Nswap2L chooses which physical device will store data based on cluster resource usage and the characteristics of various storage media. In addition, it migrates data from one physical device to another in response to changes in capacity and to take advantage of the strengths of different types of physical media, such as fast writes over the network and fast reads from flash. Performance results of our prototype implementation of Nswap2L added as a swap device on a 12 node Linux cluster show speed-ups of over 30 times versus swapping to disk and over 1.7 times versus swapping to flash. In addition, we show that for parallel benchmarks, Nswap2L using Network RAM and a flash device that is slower than Network RAM can perform better than Network RAM alone.