An embodiment of a method includes determining a file size of each of multiple files to be included in a file system image. For each file having a file size less than a lower file size threshold of the storage device currently storing the file, the file is stashed in an alternate storage device having a throughput greater than a throughput of the current storage device. In an example embodiment, files that have sizes within a size range greater than the lower file size threshold are randomly selected for stashing in an alternate storage device. A system includes a file system image generator configured to selectively stash files based on file sizes and a lower file size threshold.