Provided are a method, system, and program for processing a request to write to a source file in a storage system. A determination is made as to whether a retention rule is provided for the source file. In response to determining that one retention rule is provided for the source file, a versioned file name is generated, wherein a versioned file comprises the source file at a point-in-time. A command is transmitted to a file system to copy the source file data to a versioned file having the generated versioned file name and the generated versioned file name is added to a retention index file. The retention index file is processed to determine whether to purge versioned files according to the retention rule provided for the source file.