The present invention extends to methods, systems, and computer program products for extending non-volatile storage at a computer system. In some embodiments, a file operation is performed on at least one shadow copy of a file that is perceived by an application to be stored on a single volume. A plurality of shadow copies of a file can be accessed using durable file identifiers that are durable across changes to other file characteristics. It is indicated back to the application that the file operation was performed on the file perceived to be stored on the single volume. Storage capabilities are enhanced through migration and/or replication of files to newly added volumes.