Document revision date: 30 March 2001

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. Compaq 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:

• Personal computers (PCs)
• Workstations
• Departmental systems
• Enterprise systems
• Data center 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 laptop and personal computers can be configured in an OpenVMS Cluster as client satellites, they are not discussed extensively in this manual. For more information about configuring PCs and laptops, see the Advanced Server for OpenVMS Concepts and Planning Guide.

Table 3-1 System Types

System Type	Useful for	Examples
Workstations	Users who require their own systems with high processor performance. Examples include users running mechanical computer-aided design, scientific analysis, and data-reduction and display applications. Workstations offer the following features: Lower cost than departmental and data center systems Small footprint Useful for modeling and imaging 2D and 3D graphics capabilities	AlphaStation DS10/XP900 AlphaStation DS20E AlphaStation ES40
Departmental systems	Midrange office computing. Departmental systems offer the following capabilities: High processor and I/O performance Supports a moderate number of users, client PCs, and workstations	AlphaServer DS10 AlphaServer DS10L AlphaServer DS20E AlphaServer ES40
Data center systems	Large-capacity configurations and highly available technical and commercial applications. Data center systems have a high degree of expandability and flexibility and offer the following features: Highest CPU and I/O performance Ability to support thousands of terminal users, hundreds of PC clients, and up to 95 workstations	AlphaServer GS60, GS80 AlphaServer GS140 AlphaServer GS160, GS320

3.4 Scalability Considerations

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 Compaq World Wide Web (WWW) 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 Compaq WWW site, use the following URL:

http://www.compaq.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-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 4-1 Interconnect Characteristics

Characteristic	Description
Throughput	The quantity of data transferred across the interconnect. Some interconnects require more processor overhead than others. For example, Ethernet and FDDI interconnects require more processor overhead than do CI or DSSI. Larger packet sizes allow higher data-transfer rates (throughput) than do smaller packet sizes.
Cable length	Interconnects range in length from 3 m to 40 km.
Maximum number of nodes	The number of nodes that can connect to an interconnect varies among interconnect types. Be sure to consider this when configuring your OpenVMS Cluster system.
Supported systems and storage	Each OpenVMS Cluster node and storage subsystem requires an adapter to connect the internal system bus to the interconnect. First consider the storage and processor I/O performance, then the adapter performance, when choosing an interconnect type.

4.2 Comparison of Interconnect Types

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

Table 4-2 Comparison of Cluster Interconnect Types

Interconnect	Maximum Throughput (Mb/s)	Hardware-Assisted Data Link1	Storage Connection	Topology	Maximum Nodes per Cluster	Maximum Length
General-purpose
ATM	155/622	No	MSCP served	Radial to a switch	96 2	2 km 3/300 m 3
Ethernet/ Fast/ Gigabit	10/100/1000	No	MSCP served	Linear or radial to a hub or switch	96 2	100 m 4/100 m 4/550 m 3
FDDI	100	No	MSCP served	Dual ring to a tree, radial to a hub or switch	96 2	40 km 5
CI	140	Yes	Direct and MSCP served	Radial to a hub	32 6	45 m
DSSI	32	Yes	Direct and MSCP served	Bus	8 7	6 m 8
Shared-storage only
Fibre Channel	1000	No	Direct 9	Radial to a switch	96 2	10 km 10 /100 km 11
SCSI	160	No	Direct 9	Bus or radial to a hub	8-16 12	25 m
Node-to-node (SCS traffic only)
MEMORY CHANNEL	800	No	MSCP served	Radial	4	3 m

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.

Table 4-3 System Support for Cluster Interconnects

Systems	CI	DSSI	FDDI	Ethernet	ATM	MEMORY CHANNEL	SCSI	Fibre Channel
AlphaServer GS160, GS320	X		X	X	X	X	X	X
AlphaServer GS60, GS80, GS140	X		X 1	X	X	X	X	X
AlphaServer ES40	X	X	X	X	X	X	X
AlphaServer DS20E, DS10L, DS10	X	X	X	X	X	X	X
AlphaStation ES40	X	X	X	X	X	X 2	X
AlphaStation DS20E	X	X	X	X	X		X
AlphaStation DS10/XP900		X	X	X	X		X
AlphaStation XP1000			X	X	X		X
AlphaServer 8400, 8200	X	X	X	X 1	X	X	X	X
AlphaServer 4100, 2100, 2000	X	X	X 1	X 1	X	X	X	X 3
AlphaServer 1000		X	X	X	X 1	X	X
AlphaServer 400		X	X	X 1			X
DEC 7000/10000	X	X	X 1	X
DEC 4000		X	X	X 1
DEC 3000			X 1	X 1			X
DEC 2000			X	X 1
VAX 6000/7000/10000	X	X	X	X
VAX 4000, MicroVAX 3100		X	X	X 1
VAXstation 4000			X	X 1

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, refer to the Compaq web site:

http://www.compaq.com

Under Products, select Servers, then AlphaServers, then the server family (for example, DS, ES, or GS), then the server model. You can then select from all supported options.

You can also select the Alpha Systems Technology Technical Information web page, from which you can access documentation, supported options, firmware updates, and the software patch service for each Alpha system model.

http://www5.compaq.com/alphaserver/technology/index.html

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