VMScluster

Last updated

A VMScluster, originally known as a VAXcluster, is a computer cluster involving a group of computers running the OpenVMS operating system. Whereas tightly coupled multiprocessor systems run a single copy of the operating system, a VMScluster is loosely coupled: each machine runs its own copy of OpenVMS, but the disk storage, lock manager, and security domain are all cluster-wide. Machines can join or leave a VMScluster without affecting the rest of the cluster. For enhanced availability, VMSclusters support the use of dual-ported disks connected to two machines or storage controllers simultaneously. With OpenVMS now ported to Alpha and IA-64 machines, the facility originally named VAXclustering was renamed to VMSclustering.

Contents

Initial release

Digital Equipment Corporation first announced VAXclusters in May 1983. At this stage, clustering required specialised communications hardware, as well as some major changes to low-level subsystems in VMS. The software and hardware were designed jointly.

At the center of each cluster was a star coupler, to which every node (computer) and data storage device in the cluster was connected by one or two pairs of CI cables. ("CI" stands for Computer Interconnect.) Each pair of cables had a transmission rate of 70 megabits per second, a high speed for that era. Using two pairs gave an aggregate transmission rate of 140 megabits per second, with redundancy in case one cable failed; the star couplers also had redundant wiring for better availability.

Each CI cable connected to its computer via a CI Port, which could send and receive packets without any CPU involvement. To send a packet, a CPU had only to create a small data structure in memory and append it to a "send" queue; similarly, the CI Port would append each incoming message to a "receive" queue. Tests showed that a VAX-11/780 could send and receive 3000 messages per second, even though it was nominally a 1-MIPS machine. The closely related Mass Storage Control Protocol (MSCP) allowed similarly high performance from the mass storage subsystem. In addition, MSCP packets were very easily transported over the CI allowing remote access to storage devices.

VAXclustering was the first clustering system to achieve commercial success, and was a major selling point for VAX systems.

Later developments

In 1986, DEC added VAXclustering support to their MicroVAX minicomputers, running over Ethernet instead of special-purpose hardware. While not giving the high-availability advantages of the CI hardware, these Local Area VAXclusters provided an attractive expansion path for buyers of low-end minicomputers.

Later versions of OpenVMS (V5.0 and later) supported "mixed interconnect" VAXclusters (using both CI and Ethernet), and VAXclustering over DSSI (Digital Systems and Storage Interconnect) and FDDI, among other transports. Eventually, as high-bandwidth wide area networking became available, clustering was extended to allow satellite data links and long-distance terrestrial links. This allowed the creation of disaster-tolerant clusters; by locating the single VAXcluster in several diverse geographical areas, the cluster could survive infrastructure failures and natural disasters.

VAXclustering was greatly aided by the introduction of terminal servers using the LAT protocol. By allowing ordinary serial terminals to access the host nodes via Ethernet, it became possible for any terminal to rapidly and easily connect to any host node. This made it much simpler to accomplish fail over of the user terminals from one node of the cluster to another.

Eventually, VAXclusters reached the point where the cluster as a whole essentially never went down. Rolling upgrades even allowed the system operators to upgrade the OpenVMS system software, shutting down, upgrading, and rebooting individual nodes while the cluster as a whole continued processing. Cluster uptimes are frequently measured in years with the current longest uptime being at least sixteen years. [1]

As mentioned above, OpenVMS now also runs on Alpha and IA-64 systems, so the term VAXcluster has been replaced by VMScluster. With Gigabit Ethernet now common and 10 Gigabit Ethernet being introduced, standard networking cables and cards are quite sufficient to support VMSclustering.

Related Research Articles

AppleTalk is a discontinued proprietary suite of networking protocols developed by Apple Inc. for their Macintosh computers. AppleTalk includes a number of features that allow local area networks to be connected with no prior setup or the need for a centralized router or server of any sort. Connected AppleTalk-equipped systems automatically assign addresses, update the distributed namespace, and configure any required inter-networking routing.

Digital Equipment Corporation, using the trademark Digital, was a major American company in the computer industry from the 1960s to the 1990s. The company was co-founded by Ken Olsen and Harlan Anderson in 1957. Olsen was president until forced to resign in 1992, after the company had gone into precipitous decline.

Ethernet Computer networking technology

Ethernet is a family of computer networking technologies commonly used in local area networks (LAN), metropolitan area networks (MAN) and wide area networks (WAN). It was commercially introduced in 1980 and first standardized in 1983 as IEEE 802.3. Ethernet has since retained a good deal of backward compatibility and has been refined to support higher bit rates, a greater number of nodes, and longer link distances. Over time, Ethernet has largely replaced competing wired LAN technologies such as Token Ring, FDDI and ARCNET.

OpenVMS Computer operating system

OpenVMS is a multi-user, multiprocessing virtual memory-based operating system (OS) designed for use in time-sharing, batch processing, and transaction processing. It was first released by Digital Equipment Corporation in 1977 as VAX/VMS for its series of VAX minicomputers. OpenVMS also runs on DEC Alpha systems and the HP Itanium-based families of computers. OpenVMS is a proprietary operating system, but source code listings are available for purchase.

Ethernet over twisted pair Ethernet physical layers using twisted-pair cables

Ethernet over twisted pair technologies use twisted-pair cables for the physical layer of an Ethernet computer network. They are a subset of all Ethernet physical layers.

A star coupler is a device that takes in an input signal and splits it into several output signals.

DECnet is a suite of network protocols created by Digital Equipment Corporation. Originally released in 1975 in order to connect two PDP-11 minicomputers, it evolved into one of the first peer-to-peer network architectures, thus transforming DEC into a networking powerhouse in the 1980s. Initially built with three layers, it later (1982) evolved into a seven-layer OSI-compliant networking protocol.

ARCNET communications protocol for local area networks

Attached Resource Computer NETwork is a communications protocol for local area networks. ARCNET was the first widely available networking system for microcomputers; it became popular in the 1980s for office automation tasks. It was later applied to embedded systems where certain features of the protocol are especially useful.

InfiniBand (IB) is a computer networking communications standard used in high-performance computing that features very high throughput and very low latency. It is used for data interconnect both among and within computers. InfiniBand is also used as either a direct or switched interconnect between servers and storage systems, as well as an interconnect between storage systems.

Quadrics supercomputer

Quadrics was a supercomputer company formed in 1996 as a joint venture between Alenia Spazio and the technical team from Meiko Scientific. They produced hardware and software for clustering commodity computer systems into massively parallel systems. Their highpoint was in June 2003 when six out of the ten fastest supercomputers in the world were based on Quadrics' interconnect. They officially closed on June 29, 2009.

RapidIO electrical connection technology

The RapidIO architecture is a high-performance packet-switched interconnect technology. RapidIO supports messaging, read/write and cache coherency semantics. RapidIO fabrics guarantee in-order packet delivery, enabling power- and area- efficient protocol implementation in hardware. Based on industry-standard electrical specifications such as those for Ethernet, RapidIO can be used as a chip-to-chip, board-to-board, and chassis-to-chassis interconnect. The protocol is marketed as: RapidIO - the unified fabric for Performance Critical Computing, and is used in many applications such as Data Center & HPC, Communications Infrastructure, Industrial Automation and Military & Aerospace that are constrained by at least one of size, weight, and power (SWaP).

Local Area Transport (LAT) is a non-routable networking technology developed by Digital Equipment Corporation to provide connection between the DECserver 90, 100, 200, 300, 500, 700 and DECserver 900 terminal servers and Digital's VAX and Alpha and MIPS host computers via Ethernet, giving communication between those hosts and serial devices such as video terminals and printers. The protocol itself was designed in such a manner as to maximize packet efficiency over Ethernet by bundling multiple characters from multiple ports into a single packet for Ethernet transport. Over time, other host implementations of the LAT protocol appeared allowing communications to a wide range of Unix and other non-Digital operating systems using the LAT protocol.

IEEE 1355 IEEE standard

IEEE Standard 1355-1995, IEC 14575, or ISO 14575 is a data communications standard for Heterogeneous Interconnect (HIC).

VAX-11

The VAX-11 is a discontinued family of minicomputers developed and manufactured by Digital Equipment Corporation (DEC) using processors implementing the VAX instruction set architecture (ISA), succeeding the PDP-11. The VAX-11/780 is the first VAX computer.

Computer network Network that allows computers to share resources and communicate with each other

A computer network is a digital telecommunications network for sharing resources between nodes, which are computing devices that use a common telecommunications technology. Data transmission between nodes is supported over data links consisting of physical cable media, such as twisted pair or fiber-optic cables, or by wireless methods, such as Wi-Fi, microwave transmission, or free-space optical communication.

PATHWORKS was the trade name used by Digital Equipment Corporation of Maynard, Massachusetts for a series of programs that eased the interoperation of Digital's minicomputers with personal computers. It was available for both Windows and Mac computer systems.

GPU cluster

A GPU cluster is a computer cluster in which each node is equipped with a Graphics Processing Unit (GPU). By harnessing the computational power of modern GPUs via General-Purpose Computing on Graphics Processing Units (GPGPU), very fast calculations can be performed with a GPU cluster.

The VAXft was a family of fault-tolerant minicomputers developed and manufactured by Digital Equipment Corporation (DEC) using processors implementing the VAX instruction set architecture (ISA). "VAXft" stood for "Virtual Address Extension, fault tolerant". These systems ran the OpenVMS operating system, and were first supported by VMS 5.4. Two layered software products, VAXft System Services and VMS Volume Shadowing, were required to support the fault-tolerant features of the VAXft and for the redundancy of data stored on hard disk drives.

The Digital Storage Systems Interconnect (DSSI) is a computer bus developed by Digital Equipment Corporation for connecting storage devices and clustering VAX systems. It was designed as a smaller and lower-cost replacement for the earlier DEC Computer Interconnect that would be more suitable for use in office environments. DSSI was superseded by Parallel SCSI.

History of computer clusters

The history of computer clusters is best captured by a footnote in Greg Pfister's In Search of Clusters: “Virtually every press release from DEC mentioning clusters says ‘DEC, who invented clusters...’. IBM did not invent them either. Customers invented clusters, as soon as they could not fit all their work on one computer, or needed a backup. The date of the first is unknown, but it would be surprising if it was not in the 1960s, or even late 1950s.”

References

Further reading