A system and method for remote asynchronous replication or mirroring of changes in a source file system snapshot in a destination replica file system using a scan (via a scanner) of the blocks that make up two versions of a snapshot of the source file system, which identifies changed blocks in the respective snapshot files based upon differences in volume block numbers identified in a scan of the logical file block index of each snapshot. Trees of blocks associated with the files are traversed, bypassing unchanged pointers between versions and walking down to identify the changes in the hierarchy of the tree. These changes are transmitted to the destination mirror or replicated snapshot. This technique allows regular files, directories, inodes and any other hierarchical structure to be efficiently scanned to determine differences between versions thereof. The changes in the files and directories are transmitted over the network for update of the replicated destination snapshot in an asynchronous (lazy write) manner. The changes are described in an extensible, system-independent data stream format layered under a network transport protocol. At the destination, source changes are used to update the destination snapshot. Any deleted or modified inodes already on the destination are moved to a temporary or “purgatory” directory and, if reused, are relinked to the rebuilt replicated snapshot directory. The source file system snapshots can be representative of a volume sub-organization, such as a qtree.

System and method for determining changes in two snapshots and for transmitting changes to destination snapshot

A multi-protocol storage appliance serves file and block protocol access to information stored on storage devices in an integrated manner for both network attached storage (NAS) and storage area network (SAN) deployments. A storage operating system of the appliance implements a file system (320) that cooperates with novel virtualization modules to provide a virtualization system (300) that “virtualizes” the storage space provided by the devices. The file system provides volume management capabilities for use in block-based access to the information stored on the devices. The virtualization system (300) allows the file system to logically organize the information as named file (324), directory (326) and virtual disk storage objects (322, 328) to thereby provide an integrated NAS and SAN appliance approach to storage by enabling file-based access to the files and directories while further enabling block-based access to the virtual disks.

Multi-protocol storage appliance that provides integrated support for file and block access protocols

A system and method for maintaining logically consistent backups using minimal data transfer are presented A system comprises a backup system having a backup storage device and one or more primary systems having mass storage devices that are to be backed up on the backup storage device The primary systems identify changes that are going to be made to the mass storage device The combined effected locations in the mass storage device of these identified changes are then captured in a static snapshot when the mass storage device is in a logically consistent state Only those data blocks changed since the last backup are then transferred to backup system The backup system can then store these changes or apply the changes to the backup storage device in order to bring the backup storage device current to a particular point in time

Backup system that takes a snapshot of the locations in a mass storage device that has been identified for updating prior to updating

A system and method for updating a replicated destination file system snapshot with changes in a source file system snapshot, facilitates construction of a new directory tree on the destination from source update information using a temporary or “purgatory” directory that allows any modified and deleted files on the destination active file system to be associated with (e.g. moved to) the purgatory directory if and until they are reused. In addition, an inode map is established on the destination that maps source inode numbers to destination inode numbers so as to facilitate building of the destination tree using inode/generation number tuples. The inode map allows resynchronization of the source file system to the destination. The inode map also allows association of two or more destination snapshots to each other based upon their respective maps with the source.

System and method for asynchronous mirroring of snapshots at a destination using a purgatory directory and inode mapping

A robust optoelectronic transceiver module which is quick, easy, and inexpensive to manufacture. The transceiver module has a main housing which consists of a potting box with potting material inserted therein. In addition, a circuit board is encased by the potting material. The circuit board has an optical subassembly mounted thereon. The optical subassembly extends outside of the potting box through a recess. Correspondingly, a recess cover is provided for forming a liquid tight seal between the recess cover, the potting box, and the optical subassembly. The module housing may be pluggable via release levers having detentes received in apertures of a receptacle and a pluggable connector of the module mated within the receptacle. The receptacle may include grounding means such as a ground clip mounted within the receptacle and a protective door to limit electromagnetic emissions.

Removable transceiver module and receptacle

We describe and prove correct a programming technique using a linked list of pages for managing the free disk pages of a file system where shadowing is the recovery technique. Our technique requires a window of only two pages of main memory for accessing and maintaining the free list, and avoids wholesale copying of free-list pages during a checkpoint or recover operation.

Shadowed management of free disk pages with a linked list

Operation of a computer system after a main memory failure is enabled by storing a read-only access shadow copy of its data structures in another memory having an independent failure mode. The shadow copy is periodically updated at a series of checkpoints. Where the data structure is a linked list, updating without recopying is enabled by prelinking the list item in the read-only list to the beginning of a second read/write list, which is appended to the first list at the next checkpoint.

Technique for enabling operation of a computer system with a consistent state of a linked list data structure after a main memory failure

The blackboard architecture is a popular structuring framework for expert systems. With this structure, an expert system is built as a collection of knowledge sources which are scheduled by a controller and communicate through a shared data region, called a blackboard. The performance of such a system may be significantly enhanced by the concurrent execution of the knowledge sources. However, introduction of concurrent execution into blackboard systems requires extension of the architecture with new mechanisms for scheduling knowledge source activities, synchronizing knowledge source interactions, and accessing shared data. This paper describes our design for transaction-based facilities supporting parallel execution of knowledge sources in a blackboard system.

Transactional blackboards

Publisher Summary Statistical computing and data analysis belong among the sciences whose fundamental function is to describe the way things behave. Typically, useful descriptions emerge from the interaction between theory and experiment. This chapter (1) discusses the organization of data for statistical computing, that is, the data should be organized in structures whose basic units are modules, which are comprised of chips performing the various functions outlined in the chapter, (2) describes briefly the experimental data manipulation system to test the usefulness of these structures, and (3) discusses some of the programs that are being interfaced with the present phase of the system. The present measurements of system performance and usefulness are entirely qualitative and some quantitative data is needed to be obtained. These data must come from statistics of use, which will allow the evaluation of types of data structures used and operations performed. This, in time, will lead to the re-evaluation of the basic structure components, the recognition of the general statistical applicability of specific data structures, and a greater efficiency in data-system operations.

John D. Gabbe

Papers

Shadowed management of free disk pages with a linked list

Technique for enabling operation of a computer system with a consistent state of a linked list data structure after a main memory failure

Transactional blackboards

An experimental data structure for statistical computing