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

Abstraction and specification in program development

A file system layout apportions an underlying physical volume into one or more virtual volumes (vvols) of a storage system. The underlying physical volume is an aggregate comprising one or more groups of disks, such as RAID groups, of the storage system. The aggregate has its own physical volume block number (pvbn) space and maintains metadata, such as block allocation structures, within that pvbn space. Each vvol has its own virtual volume block number (vvbn) space and maintains metadata, such as block allocation structures, within that vvbn space. Notably, the block allocation structures of a vvol are sized to the vvol, and not to the underlying aggregate, to thereby allow operations that manage data served by the storage system (e.g., snapshot operations) to efficiently work over the vvols. The file system layout extends the file system layout of a conventional write anywhere file layout system implementation, yet maintains performance properties of the conventional implementation.

Extension of write anywhere file system layout

A system and method for improving the efficiency of the transmission of updated blocks generated by logging all the block allocations and deletes as well as CPs and PCPI creation and deletion in a persistent log. The log is scanned during each update cycle (in which changes are transmitted to a destination mirror) by the storage operating system, and only changed blocks that are referenced by the file system as it existed at the end of the update cycle or referenced by PCPIs that existed at the end of the update cycle are actually sent in the transmission. This reduces the number of changes being transmitted.

System and method for supporting asynchronous data replication with very short update intervals

Object naming and location schemes are of vital importance in an open distributed system, since they provide the basis for all interactions between objects in distributed applications. In this paper we present the COMET naming scheme, which is tailored to an open environment. This naming scheme is complemented by a location scheme, that ensures efficient mapping of location-independent names on object addresses.

Location-independent object invocation in open distributed systems

The ability to change the physical location of objects is considered indispensable in today's highly distributed computing world. As a direct offspring of process migration, object-oriented operating systems now offer object migration as a core mechanism. These systems usually equate migration with a change in physical location. Location is only one attribute whose changes are worth considering. Other attributes evolve as well during the lifetime of an object. Examples include changes in state representation and failure handling semantics. All such attribute changes can be integrated within a generalized object migration model. This results in an N-dimensional space, the object habitat, where object migration is expressed in terms of coordinate changes. This paper introduces the habitat model, and illustrates its application within the COMET heterogeneous distributed computing system. Within COMET, the habitat is a three-dimensional space with location, class and flavor coordinate axes. >

Object migration in a heterogeneous world-a multi-dimensional affair

XENOOPS is an eXecution ENvironment for Object-Oriented Parallel Software. It is designed for parallel computing systems with distributed memory. It offers basic mechanisms for a variety of object models. Furthermore, it supports grouping of objects, and object splitting and joining. XENOOPS offers dynamic load balancing, using a transparent migration facility. The architecture of XENOOPS gives application writers the possibility to customize the environment to their applications' needs. A prototype implementation has been built on a transputer system. >

The XENOOPS project

Distributed computing systems have received considerable attention in the last decade. Unfortunately, current research efforts are often restricted to homogeneous environments. There seems to be little attention for real-world installations, where heterogeneity is mostly the rule, rather than the exception. The Distributed Academic Computing Network Operating System, DACNOS for short, presents a general solution for running distributed applications in heterogeneous networks. The DACNOS extends local guest operating system services to provide homogeneous networking functionality. This is achieved by a virtual global object space, to which each user has access from within his native environment. This paper describes the architecture of the DACNOS network operating system, with special emphasis on its incarnation on the UNIX platform. It presents the DACNOS solutions to the problems of communication, access protection and data representation in a network of cooperating heterogeneous systems. DACNOS implementations currently exist for VM/CMS, VAX/VMS, PC-DOS, OS/2 and UNIX System V derivatives.

Herman Moons

Papers

Location-independent object invocation in open distributed systems

Object migration in a heterogeneous world-a multi-dimensional affair

The XENOOPS project

Distributed computing in heterogeneous environments

The design of the HERMIX distributed system