Disk doubler company, Programmed Logic Corp of Somerset, New Jersey, released SnapShot, its Unix file system module for the StackFS Stackable File System file on March 15. Snapshot freezes versions of a file while enabling a second version to be modified. StackFS is Programmed Logic’s pseudo-file system architecture enabling features to be layered on top of existing file systems without having to modify the underlying operating system. Instead of managing data on a disk, StackFS adds services such as Snapshot on top of existing file systems. Adding new file systems to working file systems, preserving data integrity and compatibility with existing file formats are therefore avoided, it claims. StackFS appears like any other file system mounted on top of different parts of a file system hierarchy. Applications access files through StackFS, which in turn forwards file operations to the underlying file system. Based on an object- oriented, stackable file system module, it works much like commands in a shell pipeline, the company says. SnapShot and other modules can be combined to provide additional semantics for existing file systems. SnapShot is mounted over other file system types such as Programmed Logic’s High Throughput File System. Other StackFS modules work by intercepting all attempts to access files within a snapshot and saving copies of the original contents of a file before applying any changes to that file. Access to files through SnapShot is translated into access to files in the underlying file system or in a save area. Privately- owned Programmed Logic, staffed by a bunch of ex-Bell Labs and Unix System Labs employees, claims it has a bunch of StackFS OEM customers in hand. As well as its TeraFile Unix file system, which provides 32-bit access to files larger than 2Gb size, other modules in the pipe will be used to merge multiple parts of a file system tree (now in beta test), file mirroring and a caching semantics. SnapShot is up on most Unix servers; prices start at $2,000. Clients cost from $500. Programmed Logic has released the third generation of its High Throughput File System journaling file system, including a DTP core compression plug-in. It’s up under UnixWare 2.x at from $2,000 per server. Solaris and System V.4 MP versions are to follow.
