Persistent File System [PFS] Technology: File management for PCs.

While PC prices fall and storage capacities continue to skyrocket each year (if not month), file system technology and management has remained fairly stagnant. Advances have been confined to longer file names and the ability to handle added security. Data management, for the most part, remains limited to often cumbersome backup applications.

Keeping track of files has always been a challenge, but add to the mix the proliferation of removable media that the industry has seen over the past few years and the need for efficient, easy-to-use data management becomes critical. File management and storage used to mean floppy disks. Today, users grapple not so much with how to store data, but how to track and access-quickly--the multitude of files on removable hard drives, tape drives, Zip drives, DVD, the clik! drive, and soon, next-generation microdrives and beyond. Individual and organizational users are finding it can take more time to find a file than it does to use the information from it.

Logical Device

The most recent development in data management is Persistent File System (PFS) technology. Developed to simplify access to mass storage devices, the patented PFS technology is particularly suitable for drive-letter addressable removable media devices such as tapes, removable hard disks, floppy disks, and CD-R devices. PFS consolidates all files and folders--whether online or not--into a single file system view by creating a virtual connection to all system storage resources. PFS, then, presents itself to Windows 95/98/NT/2000 as a logical device with standard drive-letter access, even though PFS is not a physical device.

At the heart of PFS technology is a relational database that stores name-space information for all locally attached storage devices. The PFS database is not simply a passive file list, but incorporates interceptor modules to gather name-space information from the storage devices and provide virtual I/O functionality to the storage system. The interceptor modules make user access possible through a standard drive letter to all storage devices.

Also incorporated into PFS is an Information Management Process (IMP), a task-specific, modular application that manages essential PFS functions, including configuration and database viewing tasks, as well as the movement of data from one device to another. IMPs add flexibility to PFS, which handles information management tasks for the IMPs. In application use, the IMPs function as a viewer to simplify finding files and to configure the system (See Fig).

The PFS relational database can be used to implement the directory for the removable storage device. In addition to the name-space information and required metadata, file allocation tables can also be implemented using the PFS database. For example, with tape drives, the directory database is located at the beginning of the tape and is immediately copied to hard disk when a tape is mounted. Whether tape or other piece of removable media, the directory database also is maintained by the PES so that files can be found without needing to mount the device.

Backup And Restore Functionality

When integrated with a backup system, PFS users can access all backed-up data with standard file system access. Backups can be scheduled on intervals as short as one minute, insuring that data loss can be minimized.

Since the PFS maintains all directory information online, removable media can be used more efficiently. Not only can users find any file and make file selections without mounting any piece of media, the PFS tells the user which tape or disk to load. When that tape or disk is loaded, PES can seek directly to the file.

When a backup system is implemented with a fully functional file system, PES technology allows availability of all files without the use of a separate restore application. All files backed up, regardless of the media on which they are stored, are available through Explorer or any application's "file open" dialogs. Past file versions can be retrieved via the file's context menu with a list of all backed-up versions of the file.

With a backup and restore IMP and directory viewer functionality, the PFS catalog drive-letter access allows access to all removable media used in the system, including tape drives. Since all backed-up file information is available through the PFS drive letter, a file restore IMP can build a coherent view.

The restore IMP avoids a series of total and incremental backups by showing the user a view of the system not only as it exists on hard disk, but also at any point in time. When the user selects the file set to restore, the removable media's restore IMP analyzes and determines the specific tape or disk required and the sequence of files. It, then, proceeds to retrieve the files, stopping to prompt the user if a new piece of media is required. In addition, since the PFS integrates all removable media under a single drive letter, users can integrate data protection strategies across a variety of media. Since the architecture of PFS is extensible, as is the underlying database technology, a richer data management envronment can be created and extended from locally attached storage to network and Internet servers.

David Howard is the CEO at 1 Vision Software (Loveland, CO).