The design and implementation of some persistent object stores rely on the availability of memory mapped files. A significant difficulty faced by this approach is that the programmer has very little control over when I/O occurs. In this paper, a mechanism for exposing the I/O activity of a memory mapped file is presented. This involves implementing a special purpose NFS server that provides a shadow paged file which can be memory mapped by a persistent object store. Some initial performance figures are presented to indicate the relative performance of this approach compared to more traditional approaches.