HP OpenVMS Systems Documentation

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.

This chapter provides information to help you select systems for your OpenVMS Cluster to satisfy your business and application requirements.

3.1 Alpha and VAX Architectures

An OpenVMS Cluster can include systems running OpenVMS Alpha, OpenVMS VAX, or both. HP provides a full range of systems for both the Alpha and VAX architectures.

• OpenVMS Alpha operating system
  Based on a 64-bit RISC (reduced instruction set computing) architecture, OpenVMS Alpha provides industry-leading price/performance benefits with standard I/O subsystems for flexibility and expansion.
• OpenVMS VAX operating system
  Based on a 32-bit CISC (complex instruction set computing) architecture, OpenVMS VAX provides high CISC performance and a rich, powerful instruction set. OpenVMS VAX also supports a wide variety of standard I/O subsystems.

Alpha and VAX systems span a range of computing environments, including:

• Workstations
• Midrange systems
• Enterprise systems

Your choice of systems depends on your business, your application needs, and your budget. With a high-level understanding of systems and their characteristics, you can make better choices.

Table 3-1 is a comparison of recently shipped OpenVMS Cluster systems. While a cluster can provide services to Windows and MS-DOS laptop and personal computers, this topic is not discussed extensively in this manual. For more information about configuring a cluster to serve PCs and laptops, consult your HP representative.

When you choose a system based on scalability, consider the following:

• Maximum processor capacity
• Maximum memory capacity
• Maximum storage capacity

The OpenVMS environment offers a wide range of alternative ways for growing and expanding processing capabilities of a data center, including the following:

• Many Alpha and VAX systems can be expanded to include additional memory, processors, or I/O subsystems.
• You can add systems to your OpenVMS Cluster at any time to support increased work load. The vast range of systems, from small workstation to high-end symmetric multiprocessing (SMP) systems, can interconnect and be reconfigured easily to meet growing needs.
• You can add storage to your OpenVMS Cluster system by increasing the quantity and speed of disks, CD-ROM devices, and tapes.
  Reference: For more information about storage devices, see Chapter 5.

Reference: For more information about scalability, see Chapter 10.

3.5 Availability Considerations

An OpenVMS Cluster system is a highly integrated environment in which multiple systems share access to resources. This resource sharing increases the availability of services and data. OpenVMS Cluster systems also offer failover mechanisms that are transparent and automatic, and require little intervention by the system manager or the user.

Reference: See Chapter 8 and Chapter 9 for more information about these failover mechanisms and about availability.

3.6 Performance Considerations

The following factors affect the performance of systems:

• Applications and their performance requirements
• The number of users that the system must support
• The type of storage subsystem that you require

With these requirements in mind, compare processor performance, I/O throughput, memory capacity, and disk capacity in the Alpha and VAX specifications that follow.

3.7 System Specifications

The HP web site provides ordering and configuring information for Alpha and Intel workstations and servers. It also contains detailed information about storage devices, printers, and network application support.

To access the HP web site, use the following URL:

http://www.hp.com/

An interconnect is a physical path that connects computers to other computers, and to storage subsystems. OpenVMS Cluster systems support a variety of interconnects (also referred to as buses) so that members can communicate with each other and with storage, using the most appropriate and effective method available.

The software that enables OpenVMS Cluster systems to communicate over an interconnect is the System Communications Services (SCS). An interconnect that supports node-to-node SCS communications is called a cluster interconnect. An interconnect that provides node-to-storage connectivity within a cluster is called a shared-storage interconnect. Some interconnects, such as CI and DSSI, can serve as both cluster and storage interconnects.

OpenVMS supports the following types of interconnects:

• Cluster interconnects (node to node only)
  • Ethernet (10/100, Gigabit)
  • Asynchronous transfer mode (ATM)
  • FDDI (Fiber Distributed Data Interface)
  • MEMORY CHANNEL
  • Shared Memory CI (SMCI) (Galaxy instance to Galaxy instance)
• Shared-storage interconnects (node to storage only)
  • Fibre Channel
  • SCSI (Small Computer Systems Interface)
• Both node-to-node and node-to-storage interconnects
  • CI (computer interconnect)
  • DSSI (Digital Storage Systems Interconnect)

The interconnects described in this chapter share some general characteristics. Table 4-1 describes these characteristics.

Table 4-2 shows key statistics for a variety of interconnects.

You can use multiple interconnects to achieve the following benefits:

• Failover
  If one interconnect or adapter fails, the node communications automatically move to another interconnect.
• MSCP server load balancing
  In a multiple MSCP server configuration, an OpenVMS Cluster performs load balancing to automatically choose the best path. This reduces the chances that a single adapter could cause an I/O bottleneck. Depending on your configuration, multiple paths from one node to another node may transfer more information than would a single path.
  Reference: See Section 10.7.3 for an example of dynamic MSCP load balancing.

A mixed interconnect is a combination of two or more different types of interconnects in an OpenVMS Cluster system. You can use mixed interconnects to combine the advantages of each type and to expand your OpenVMS Cluster system. For example, an Ethernet cluster that requires more storage can expand with the addition of Fibre Channel, SCSI, or CI connections.

4.5 Interconnects Supported by Alpha and VAX Systems

Table 4-3 shows the OpenVMS Cluster interconnects supported by Alpha and VAX systems.

You can also refer to the most recent OpenVMS Cluster SPD to see the latest information on supported interconnects.

As Table 4-3 shows, OpenVMS Clusters support a wide range of interconnects. The most important factor to consider is how much I/O you need, as explained in Chapter 2.

In most cases, the I/O requirements will be less than the capabilities of any one OpenVMS Cluster interconnect. Ensure that you have a reasonable surplus I/O capacity, then choose your interconnects based on other needed features.

Reference: For detailed information about the interconnects and adapters supported on each AlphaServer system, go to the OpenVMS web page at:

http://hp.com/go/openvms

Select AlphaSystems (from the left navigation panel under related links). Then select the AlphaServer system of interest and its QuickSpecs. The QuickSpecs for each AlphaServer system briefly describe all options, including the adapters, supported on that system.