Document revision date: 15 July 2002

The System Communications Architecture (SCA) defines the communications mechanisms that allow nodes in an OpenVMS Cluster system to cooperate. It governs the sharing of data between resources at the nodes and binds together System Applications (SYSAPs) that run on different Alpha and VAX computers.

SCA consists of the following hierarchy of components:

Communications Software	Function
System applications (SYSAPs)	Consists of clusterwide applications (for example, disk and tape class drivers, connection manager, and MSCP server) that use SCS software for interprocessor communication.
System Communications Services (SCS)	Provides basic connection management and communication services, implemented as a logical path, between system applications (SYSAPs) on nodes in an OpenVMS Cluster system.
Port drivers	Control the communication paths between local and remote ports.
Physical interconnects	Consists of ports or adapters for CI, DSSI, Ethernet (10/100 and Gigabit), ATM, FDDI, and MEMORY CHANNEL interconnects.

1.4.1 System Communications

Figure 1-1 shows the interrelationships between the OpenVMS Cluster components.

Figure 1-1 OpenVMS Cluster System Communications

In Figure 1-1, processes in different nodes exchange information with each other:

• Processes can call the $QIO system service and other system services directly from a program or indirectly using other mechanisms such as OpenVMS Record Management Services (RMS). The $QIO system service initiates all I/O requests.
• A SYSAP on one OpenVMS Cluster node must communicate with a SYSAP on another node. For example, a connection manager on one node must communicate with the connection manager on another node, or a disk class driver on one node must communicate with the MSCP server on another node.
• The following SYSAPs use SCS for cluster communication:
  • Disk and tape class drivers
  • MSCP server
  • TMSCP server
  • DECnet class driver
  • Connection manager
• SCS routines provide services to format and transfer SYSAP messages to a port driver for delivery over a specific interconnect.
• Communications go through the port drivers to OpenVMS Cluster computers and storage controllers. The port driver manages a logical path, called a virtual circuit, between each pair of ports in an OpenVMS Cluster system.

Applications running on OpenVMS Cluster systems use DECnet or TCP/IP (transmission control protocol and internet protocol) for application communication. The DECnet and TCP/IP communication services allow processes to locate or start remote servers and then exchange messages.

Note that generic references to DECnet in this document mean either DECnet for OpenVMS or DECnet--Plus (formerly known as DECnet/OSI) software.

1.4.3 Cluster Alias

A DECnet feature known as a cluster alias provides a collective name for the nodes in an OpenVMS Cluster system. Application software can connect to a node in the OpenVMS Cluster using the cluster alias name rather than a specific node name. This frees the application from keeping track of individual nodes in the OpenVMS Cluster system and results in design simplification, configuration flexibility, and application availability.

1.5 System Management

The OpenVMS Cluster system manager must manage multiple users and resources for maximum productivity and efficiency while maintaining the necessary security.

1.5.1 Ease of Management

An OpenVMS Cluster system is easily managed because the multiple members, hardware, and software are designed to cooperate as a single system:

• Smaller configurations usually include only one system disk (or two for an OpenVMS Cluster configuration with both OpenVMS VAX and OpenVMS Alpha operating systems), regardless of the number or location of computers in the configuration.
• Software needs to be installed only once for each operating system (VAX and Alpha), and is accessible by every user and node of the OpenVMS Cluster.
• Users need to be added once to have access to the resources of the entire OpenVMS Cluster.
• Several system management utilities and commands facilitate cluster management.

Figure 1-2 illustrates centralized system management.

Figure 1-2 Single-Point OpenVMS Cluster System Management

The OpenVMS operating system supports a number of utilities and tools to assist you with the management of the distributed resources in OpenVMS Cluster configurations. Proper management is essential to ensure the availability and performance of OpenVMS Cluster configurations.

OpenVMS and its partners offer a wide selection of tools to meet diverse system management needs. Table 1-1 describes the Compaq products available for cluster management and indicates whether each is supplied with the operating system or is an optional product. Table 1-2 describes some of the most important utilities and tools produced by OpenVMS partners for managing an OpenVMS Cluster configuration.

Table 1-1 System Management Tools

Tool	Supplied or Optional	Function
Accounting
VMS Accounting	Supplied	Tracks how resources are being used.
Configuration and capacity planning
LMF (License Management Facility)	Supplied	Helps the system manager to determine which software products are licensed and installed on a standalone system and on each of the computers in an OpenVMS Cluster system.
Graphical Configuration Manager (GCM)	Supplied	A portable client/server application that gives you a way to view and control the configuration of partitioned AlphaServer systems running OpenVMS.
Galaxy Configuration Utility (GCU)	Supplied	A DECwindows Motif application that allows system managers to configure and manage an OpenVMS Galaxy system from a single workstation window.
SYSGEN (System Generation) utility	Supplied	Allows you to tailor your system for a specific hardware and software configuration. Use SYSGEN to modify system parameters, load device drivers, and create additional page and swap files.
CLUSTER_CONFIG.COM	Supplied	Automates the configuration or reconfiguration of an OpenVMS Cluster system and assumes the use of DECnet.
CLUSTER_CONFIG_LAN.COM	Supplied	Automates configuration or reconfiguration of an OpenVMS Cluster system without the use of DECnet.
Compaq Management Agents for OpenVMS	Supplied	Consists of a web server for system management with management agents that allow you to look at devices on your OpenVMS systems.
Compaq Insight Manager XE	Supplied with every Compaq NT server	Centralizes system management in one system to reduce cost, improve operational efficiency and effectiveness, and minimize system down time. You can use Compaq Insight Manager XE on an NT server to monitor every system in an OpenVMS Cluster system. In a configuration of heterogeneous Compaq systems, you can use Compaq Insight Manager XE on an NT server to monitor all systems.
Event and fault tolerance
OPCOM message routing	Supplied	Provides event notification.
Operations management
Clusterwide process services	Supplied	Allows OpenVMS system management commands, such as SHOW USERS, SHOW SYSTEM, and STOP/ID=, to operate clusterwide.
Availability Manager	Supplied	From either an OpenVMS Alpha or a Windows node, enables you to monitor one or more OpenVMS nodes on an extended local area network (LAN). Availability Manager collects system and process data from multiple OpenVMS nodes simultaneously, then analyzes the data, and displays the output using a native Java GUI.
DECamds	Supplied	Collects and analyzes data from multiple nodes simultaneously, directing all output to a centralized DECwindows display. The analysis detects resource availability problems and suggests corrective actions.
SCACP (Systems Communications Architecture Control Program)	Supplied	Enables you to monitor and manage switched LAN paths.
DFS (Distributed File Service)	Optional	Allows disks to be served across a LAN or WAN.
DNS (Distributed Name Service)	Optional	Configures certain network nodes as name servers that associate objects with network names.
LATCP (Local Area Transport Control Program)	Supplied	Provides the function to control and obtain information from the LAT port driver.
LANCP (LAN Control Program)	Supplied	Allows the system manager to configure and control the LAN software on OpenVMS systems.
NCP (Network Control Protocol) utility	Optional	Allows the system manager to supply and access information about the DECnet for OpenVMS (Phase IV) network from a configuration database.
NCL (Network Control Language) utility	Optional	Allows the system manager to supply and access information about the DECnet--Plus network from a configuration database.
OpenVMS Management Station	Supplied	Enables system managers to set up and manage accounts and print queues across multiple OpenVMS Cluster systems and OpenVMS nodes. OpenVMS Management Station is a Microsoft Windows and Windows NT based management tool.
POLYCENTER Software Installation Utility (PCSI)	Supplied	Provides rapid installations of software products.
Queue Manager	Supplied	Uses OpenVMS Cluster generic and execution queues to feed node-specific queues across the cluster.
Show Cluster utility	Supplied	Monitors activity and performance in an OpenVMS Cluster configuration, then collects and sends information about that activity to a terminal or other output device.
SDA (System Dump Analyzer)	Supplied	Allows you to inspect the contents of memory as saved in the dump taken at crash time or as it exists in a running system. You can use SDA interactively or in batch mode.
SYSMAN (System Management utility)	Supplied	Enables device and processor control commands to take effect across an OpenVMS Cluster.
VMSINSTAL	Supplied	Provides software installations.
Performance
AUTOGEN utility	Supplied	Optimizes system parameter settings based on usage.
Monitor utility	Supplied	Provides basic performance data.
Security
Authorize utility	Supplied	Modifies user account profiles.
SET ACL command	Supplied	Sets complex protection on many system objects.
SET AUDIT command	Supplied	Facilitates tracking of sensitive system objects.
Storage management
Backup utility	Supplied	Allows OpenVMS Cluster system managers to create backup copies of files and directories from storage media and then restore them. This utility can be used on one node to back up data stored on disks throughout the OpenVMS Cluster system.
Mount utility	Supplied	Enables a disk or tape volume for processing by one computer, a subset of OpenVMS Cluster computers, or all OpenVMS Cluster computers.
Volume Shadowing for OpenVMS	Optional	Replicates disk data across multiple disks to help OpenVMS Cluster systems survive disk failures.

1.5.3 System Management Tools from OpenVMS Partners

OpenVMS Partners offer a wide selection of tools to meet diverse system management needs, as shown in Table 1-2. The types of tools are described in the following list:

• Schedule managers
  Enable specific actions to be triggered at determined times, including repetitive and periodic activities, such as nightly backups.
• Event managers
  Monitor a system and report occurrences and events that may require an action or that may indicate a critical or alarming situation, such as low memory or an attempted security breakin.
• Console managers
  Enable a remote connection to and emulation of a system console so that system messages can be displayed and commands can be issued.
• Performance managers
  Monitor system performance by collecting and analyzing data to allow proper tailoring and configuration of system resources. Performance managers may also collect historical data for capacity planning.

Table 1-2 System Management Products from OpenVMS Partners

Business Partner	Product	Type or Function
BMC	Perform and Predict	Performance and capacity manager
	Patrol for OpenVMS	Event manager
	ControlM	Console manager
Computer Associates	Advise IT	Performance manager
	Command IT	Console manager
	Schedule IT	Schedule manager
	Watch IT	Event manager
	Unicenter TNG	Package of various products
Fortel	ViewPoint	Performance manager
Global Maintech	VCC	Console manager
Heroix	RoboMon	Event manager
	RoboCentral	Console manager
ISE	Schedule	Schedule manager
Ki NETWORKS	CLIM	Console manager
ORSYP	Dollar Universe	Schedule manager
RAXCO	Perfect Cache	Storage performance
	Perfect Disk	Storage management
TECsys Development Inc.	Console Works	Console manager

For current information about OpenVMS Partners and the tools they provide, visit the following web site: http://www.openvms.compaq.com/openvms/system_management.html

1.5.4 Other Configuration Aids

In addition to these utilities and partner products, several commands are available that allow the system manager to set parameters on HSC, HSJ, HSD, HSZ, HSG, and RF subsystems to help configure the system. See the appropriate hardware documentation for more information.

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