A segmented object storage system is an object storage system that divides files into a number of object segments, each segment corresponding to a portion of an object, and stores each segment individually in the storage system. The system also generates and stores a manifest file describing the relationship of the various segments to the original data file. Requests to retrieve the segmented file are fulfilled by consulting the manifest file and using the information from the manifest to reconstitute the original data file from the constituent segments. Modifying, appending to, or truncating the object is accomplished by manipulating individual segments and the manifest file. Manipulation of the individual object segments and/or the manifest can be used to implement copy-on-write, snapshotting, software transactional memory, and peer-to-peer transmission of the large file.