VAX 4000 Dual-Host Systems

This document, "VAX 4000 Dual-Host Systems," describes the configuration, components, benefits, and requirements for implementing dual-host systems using VAX 4000 series computers, or a VAX 4000 with a Q-bus MicroVAX system.

Key aspects covered include:

• Definition: A dual-host configuration connects two systems via a Digital Storage Systems Interconnect (DSSI) bus, allowing them to share Integrated Storage Elements (ISEs) for increased data availability and performance.
• Benefits: It enhances disk availability for critical applications, minimizes downtime through automatic failover (especially for VAXcluster satellites) and redundant data paths, facilitates read/write file sharing, distributed resource sharing, and provides a growth path with improved I/O capabilities.
• Components: Essential hardware includes RF-series ISEs (disk drives), R400X expanders (for additional ISEs), external DSSI cables, and DSSI adapters (Embedded DSSI Adapter or KFQSA).
• Requirements: Dual-host systems necessitate VAX/VMS version 5.3-2 or later, along with VAXcluster and DECnet software licenses, and Ethernet hardware. Specific rules apply to the number of ISEs and system enclosures per DSSI bus.
• Configurations: The manual provides an overview of dual-host concepts and basic requirements in Chapter 1, while Chapter 2 details and illustrates various supported VAX 4000 dual-host configurations with diagrams.

Overall, it serves as a reference guide for planning and understanding high-availability VAX 4000 computing environments.