Abstract: A file system uses a virtual node architecture to create a three-dimensional directory. A virtual node is created for each file and directory. Selected directory nodes can be linked together to create a stack. Only the top directory in each stack is normally accessible and appears to contain a union of all files and subdirectories contained in the stack. A look-up procedure is used to find a specified file or directory name by sequentially searching the stack beginning with the top directory node and returning the node corresponding to the first occurrence of the name encountered in the search. The virtual node architecture allows the present system to accommodate diverse file systems by permitting each node to designate an individual physical file storage system. The present system can also copy files and directory nodes contained in one stack node to another stack node for the purposes of file back-up or caching.

Abstract: A system that places a statistical collection routine, which tracks file usage, within the path lookup process of an operating system. A statistic summarization process runs as a task of the operating system and periodically accesses the statistics collected by the statistics collection routine and updates a database. A file migration process is scheduled to run periodically to examine the database information. Files that have a predetermined usage during the time may be migrated, based on user criteria, between a primary, high speed, storage device and a secondary, slow speed, storage device. The secondary storage device might be a network file server attached to a local area network, a read-only device, or other storage device.