HP OpenVMS Systems Documentation

OpenVMS Cluster Systems

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:

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.

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.

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.