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

3.1 Integrity servers and Alpha Systems

An OpenVMS cluster can include systems running OpenVMS Integrity servers or a combination of systems running OpenVMS Integrity servers and OpenVMS Alpha. See the OpenVMS Software Product Description for a listing of the models currently supported.

• OpenVMS Integrity servers operating system
  Based on the Intel Itanium architecture, OpenVMS Integrity servers provide the price or performance, reliability, and scalability benefits of OpenVMS on the industry-standard HP Integrity server systems.
• OpenVMS Alpha operating system
  Based on a 64-bit RISC (reduced instruction set computing) architecture, OpenVMS Alpha provides industry-leading price or performance benefits with standard I/O subsystems for flexibility and expansion.

HP Integrity server systems span a range of computing environments, including:

• Entry
• Standalone servers
• Scalable blades
• Integrity VM guest 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. See the Software Product Description or visit http://www.hp.com/go/openvms for the complete list of supported Integrity server systems.

3.4 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 for more information about these failover mechanisms and about availability.

3.5 System Specifications

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

To access the HP web site, visit:

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.

OpenVMS supports the following types of interconnects:

• Cluster interconnects (node-to-node only)
  • Ethernet
  • Fast Ethernet
  • Gigabit Ethernet
  • 10 Gigabit Ethernet (Integrity severs only)
• Shared-storage interconnects (node-to-storage only)
  • Fibre Channel
  • Small Computer Systems Interface (SCSI) (Integrity servers or Alpha, Integrity servers limited to specific configurations)
  • Serial Attached SCSI (SAS) (Integrity servers only)
• Both node-to-node and node-to-storage interconnects
  • Ethernet, Fast Ethernet, Gigabit Ethernet
  • 10 Gigabit Ethernet (Integrity servers only)

  Note Cluster over IP is supported on Ethernet, Fast Ethernet, Gigabit Ethernet, and 10 Gigabit Ethernet.

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 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
Ethernet Fast Gigabit 10 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
Shared-storage only
Fibre Channel	1000	No	Direct 5	Radial to a switch	96 2	10 km 6 /100 km 7
SCSI	160	No	Direct 5	Bus or radial to a hub	8-12 8	25 m
SAS	6000	No	Direct	Point to Point, Radial to a switch	96 2	6 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 9.3.3 for an example of dynamic MSCP load balancing.

You can use two or more different types of interconnects in an OpenVMS Cluster system. You can use different types of interconnects to combine the advantages of each type and to expand your OpenVMS Cluster system.

For the latest information on supported interconnects, see the most recent OpenVMS Cluster Systems SPD.

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

http://www.hp.com/go/openvms

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

Select HP 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.

4.6 Fibre Channel Interconnect

Fibre Channel is a high-performance ANSI standard network and storage interconnect for PCI-based Alpha systems. It is a full-duplex serial interconnect and can simultaneously transmit and receive over 100 megabytes per second. Fibre Channel supports simultaneous access of SCSI storage by multiple nodes connected to a Fibre Channel switch. A second type of interconnect is needed for node-to-node communications.

4.6.1 Advantages

The Fibre Channel interconnect offers the following advantages:

• High-speed transmission, 2 Gb/s, 4 Gb/s, 8 Gb/s (depending on adapter)
• Scalable configuration to support department to enterprise configurations.
• Long-distance interconnects
  Fibre Channel supports multimode fiber at 500 meters per link. Fibre Channel supports longer-distance interswitch links (ISLs) --- up to 100 kilometers per link, using single-mode fiber and up to 600 kilometers per link with FC/ATM links.
  In addition, SANworks Data Replication Manager (DRM) configurations provide long distance ISLs through the use of the Open Systems Gateway and Wave Division Multiplexors.
• High availability
  Multipath support is available to provide configurations with no single point of failure.

The Fibre Channel interconnect transmits up to 2 Gb/s, 4 Gb/s, 8 Gb/s (depending on adapter). It is a full-duplex serial interconnect that can simultaneously transmit and receive over 100 MB/s.

4.7 MEMORY CHANNEL Interconnect (Alpha Only)

MEMORY CHANNEL is a high-performance cluster interconnect technology for PCI-based Alpha systems. With the benefits of very low latency, high bandwidth, and direct memory access, MEMORY CHANNEL complements and extends the unique ability of OpenVMS Clusters to work as a single, virtual system.

Three hardware components are required by a node to support a MEMORY CHANNEL connection:

• A PCI-to-MEMORY CHANNEL adapter
• A link cable (3 m or 10 feet long)
• A port in a MEMORY CHANNEL hub (except for a two-node configuration in which the cable connects just two PCI adapters)

A MEMORY CHANNEL hub is a PC size unit that provides a connection among systems. MEMORY CHANNEL can support up to four Alpha nodes per hub. You can configure systems with two MEMORY CHANNEL adapters in order to provide failover in case an adapter fails. Each adapter must be connected to a different hub.

A MEMORY CHANNEL hub is not required in clusters that comprise only two nodes. In a two-node configuration, one PCI adapter is configured, using module jumpers, as a virtual hub.

4.7.1 Advantages

MEMORY CHANNEL technology provides the following features:

• Offers excellent price or performance.
  With several times the CI bandwidth, MEMORY CHANNEL provides a 100 MB/s interconnect with minimal latency. MEMORY CHANNEL architecture is designed for the industry-standard PCI bus.
• Requires no change to existing applications.
  MEMORY CHANNEL works seamlessly with existing cluster software, so that no change is necessary for existing applications. The new MEMORY CHANNEL drivers, PMDRIVER and MCDRIVER, integrate with the System Communications Services layer of OpenVMS Clusters in the same way that existing port drivers do. Higher layers of cluster software are unaffected.
• Offloads CI, DSSI, and the LAN in SCSI clusters.
  You cannot connect storage directly to MEMORY CHANNEL, but you can use it to make maximum use of each interconnect's strength.
  While MEMORY CHANNEL is not a replacement for CI and DSSI, when used in combination with those interconnects, it offloads their node-to-node traffic. This enables them to be dedicated to storage traffic, optimizing communications in the entire cluster.
  When used in a cluster with SCSI and LAN interconnects, MEMORY CHANNEL offloads node-to-node traffic from the LAN, enabling it to handle more TCP/IP or DECnet traffic.
• Provides fail-separately behavior.
  When a system failure occurs, MEMORY CHANNEL nodes behave like any failed node in an OpenVMS Cluster. The rest of the cluster continues to perform until the failed node can rejoin the cluster.

The MEMORY CHANNEL interconnect has a very high maximum throughput of 100 MB/s. If a single MEMORY CHANNEL is not sufficient, up to two interconnects (and two MEMORY CHANNEL hubs) can share throughput.

4.7.3 Supported Adapter

The MEMORY CHANNEL adapter connects to the PCI bus. The MEMORY CHANNEL adapter, CCMAA--BA, provides improved performance over the earlier adapter.

Reference: For information about the CCMAA-BA adapter support on AlphaServer systems, go to the OpenVMS web page at:

http://www.hp.com/go/openvms

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

4.8 SCSI Interconnect

The SCSI interconnect is an industry standard interconnect that supports one or more computers, peripheral devices, and interconnecting components. SCSI is a single-path, daisy-chained, multidrop bus. It is a single 8-bit or 16-bit data path with byte parity for error detection. Both inexpensive single-ended and differential signaling for longer distances are available.

In an OpenVMS Cluster, multiple computers on a single SCSI interconnect can simultaneously access SCSI disks. This type of configuration is called multihost SCSI connectivity or shared SCSI storage and is restricted to certain adapters and limited configurations. A second type of interconnect is required for node-to-node communication.

Shared SCSI storage in an OpenVMS Cluster system enables computers connected to a single SCSI bus to share access to SCSI storage devices directly. This capability makes it possible to build highly available servers using shared access to SCSI storage.

4.8.1 OpenVMS Alpha Configurations

For multihost access to SCSI storage, the following components are required:

• SCSI host adapter that is supported in a multihost configuration (see Table 4-5)
• SCSI interconnect
• Terminators, one for each end of the SCSI interconnect
• Storage devices that are supported in a multihost configuration (RZnn; refer to the OpenVMS Cluster SPD [29.78.nn])

For larger configurations, the following components are available:

• Storage controllers (HSZnn)
• Bus isolators (DWZZA, DWZZB, or DWZZC) to convert single-ended to differential signaling and to effectively double the SCSI interconnect length

Reference: For a detailed description of how to connect OpenVMS Alpha SCSI configurations, see Appendix A.

4.8.2 OpenVMS Integrity servers Two-Node Shared SCSI Configuration

Shared SCSI storage support for two-node OpenVMS Integrity servers Cluster systems was introduced in OpenVMS Version 8.2-1. Prior to this release, shared SCSI storage was supported on OpenVMS Alpha systems only, using an earlier SCSI host-based adapter (HBA).

Shared SCSI storage in an OpenVMS Integrity servers Cluster system is subject to the following restrictions:

• A maximum of two OpenVMS Integrity server systems can be connected to a single SCSI bus.
• A maximum of four shared-SCSI buses can be connected to each system.
• Systems supported are the rx1600 family, the rx2600 family, and the rx4640 system.
• The A7173A HBA is the only supported HBA.
• MSA30-MI storage enclosure is the only supported SCSI storage type.
• Ultra320 SCSI disk family is the only supported disk family.

Figure 4-1 illustrates two-node shared SCSI configuration. Note that a second interconnect, a LAN, is required for host-to-host OpenVMS Cluster communications. (OpenVMS Cluster communications are also known as System Communications Architecture (SCA) communications.)

Note, the SCSI IDs of 6 and 7 are required in this configuration. One of the systems must have a SCSI ID of 6 for each A7173A adapter port connected to a shared SCSI bus, instead of the factory-set default of 7. You use the U320_SCSI pscsi.efi utility, included on the IPF Offline Diagnostics and Utilities CD, to change the SCSI ID. The procedure for doing this is documented in the HP A7173A PCI-X Dual Channel Ultra320 SCSI Host Bus Adapter Installation Guide at:

http://docs.hp.com/en/netcom.html

Figure 4-1 Two-Node OpenVMS Integrity servers Cluster System

The SCSI interconnect offers the following advantages:

• Lowest cost, shared direct access to storage
  Because SCSI is an industry standard and is used extensively throughout the industry, it is available from many manufacturers at competitive prices.
• Scalable configuration to achieve high performance at a moderate price
  You can choose:
  • Width of SCSI interconnect
    Narrow (8 bits) or wide (16 bits).
  • Transmission mode
    Single-ended signaling, the most common and least expensive, or differential signaling, which provides higher signal integrity and allows a longer SCSI interconnect.
  • Signal speed (standard, fast, or ultra mode)
  • Number of nodes sharing the SCSI bus (two or three)
  • Number of shared SCSI buses to which a node can connect (maximum of six)
  • Storage type and size (RZnn or HSZnn)
  • Computer type and size (AlphaStation or AlphaServer)

Table 4-3 show throughput for the SCSI interconnect.

Table 4-3 Maximum Data Transfer Rates in Megabytes per Second

Mode	Narrow (8-Bit)	Wide (16-Bit)
Standard	5	10
Fast	10	20
Ultra	20	40