I have recently developed DMFS, a Data Migration File System, for NetBSD[1]. This file system provides kernel support for the data migration system being developed by my research group at NASA/Ames. The file system utilizes an underlying file store to provide the file backing, and coordinates user and system access to the files. It stores its internal metadata in a flat file, which resides on a separate file system. This paper will first describe our data migration system to provide a context for DMFS, then it will describe DMFS. I also will describe the changes to NetBSD needed to make DMFS work. Then I will give an overview of the file archival and restoration procedures, and describe how some typical user actions are modified by DMFS. Lastly, I will present simple performance measurements which indicate that there is little performance loss due to the use of the DMFS layer.