Methods, systems, and apparatus, including computer programs encoded on a computer storage medium, for storing data. In one aspect, a method includes receiving a user input to present a visual representation of a first prior state of a file system; generating the first visual representation of a first prior state of the file system at a first time in the past according to a first virtual file system corresponding to that first time; presenting the first visual representation, where the first virtual file system is a reduced representation of the file system at that first time; receiving a user input to present a second visual representation of a second prior state of the file system at a second time in the past according to a second virtual file system corresponding to that second time; and presenting the second visual representation.