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Document:	MicroVAX Dual-Host Systems
Order Number:	EK-338AC-DH
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Pages:	24
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MicroVAX Dual-Host Systems

Order Number EK-338AC-DH-003

Digital Equipment Corporation
Maynard, Massachusetts

First Printing, June 1989
Second Printing, March 1990
Third Printing, December 1990
The information in this document is subject to change without notice and should not be
construed as a commitment by Digital Equipment Corporation.
Digital Equipment Corporation assumes no responsibility for any errors that may appear in
this document.
The software, if any, described in this document is furnished under a license and may be used
or copied only in accordance with the terms of such license. No responsibility is assumed
for the use or reliability of software or equipment that is not supplied by Digital Equipment
Corporation or its affiliated companies.
Restricted Rights: Use, duplication or disclosure by the U.S. Government is subject to
restrictions as set forth in subparagraph (c)(1)(ii) of the Rights in Technical Data and Computer
Software clause at DFARS 252.227-7013.
© Digital Equipment Corporation 1989,1990. All rights reserved.
Printed in U.S.A.
The Reader's Comments form at the end of this document requests your critical evaluation to
assist in preparing future documentation.
The following are trademarks of Digital Equipment Corporation:
DECnet
DECserver
DSSI
MicroVAX
Q-bus
UNIBUS
VAX
VAX 4000
VAXcluster
VAX DOCUMENT

VMS
the DIGITAL logo

FCC NOTICE: The equipment described in this manual generates, uses, and may emit radio
frequency energy. The equipment has been type tested and found to comply with the limits for
a Class A computing device pursuant to Subpart J of Part 15 of FCC Rules, which are designed
to provide reasonable protection against such radio frequency interference when operated in
a commercial· environment. Operation of this equipment in a residential area may cause
interference, in which case the user at his own expense may be required to take measures to
correct the interference.
51582

This document was prepared using VAX DOCUMENT, Version 1.2.

Contents
Preface

Chapter 1 Dual-Host Systems and DSSI
1.1 Introduction to Dual-Host Systems ................... .
1.1.1
Higher Disk Availability ......................... .
1.1.2
Minimized Downtime ............................ .
1.2 Dual-Host Components ............................ .
1.2.1
RF-Series Integrated Storage Elements .............. .
Supported Expanders ............................ .
1.2.2
External DSSI Cables ........................... .
1.2.3
1.3 DSSI Storage Bus and Adapters ..................... .
1.3.1
Embedded DSSI Adapter ......................... .
1.3.2
KFQSA ....................................... .
DSSI Adapter (EDA) .................... .
Embedded
1.3.3
1.4

1.5
1.6
1.7

Configuration Rules for Dual-Host Systems ............. .
VMS and Dual-Host Configurations ................... .
Module Order .................................... .
System Disk ..................................... .

1-1
1-1
1-2
1-2
1-2
1-3
1-3
1-3
1-4
1-4
1-4
1-5
1-6
1-6
1-6

Chapter 2 Supported MicroVAX Dual-Host Configurations
Appendix A

Related Documentation

Index

iii

Figures
2-1
2-2
2-3
2-4
2-5
2-6
2-7
2-8
2-9

Two Q-Bus MicroVAX Systems, Each Using a KFQSA
Adapter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-2
Two Q-Bus MicroVAX Systems, Each Using an EDA Adapter 2-3
Two Q-Bus MicroVAX Systems Using Mixed Adapters. . . . .. 2-4
Two Q-Bus MicroVAX Systems with EDAs and a Shared
Expander . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 2-5
Two Q-Bus MicroVAX Systems with KFQSA Adapters and
Shared Expander. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-6
Two Q-Bus MicroVAX Systems with a Shared Expander and
Mixed Adapters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-7
Two Non-DSSI MicroVAX Systems with Two DSSI Expanders 2-8
Two Q-Bus MicroVAX Systems in a Dual-DSSI, Dual-Host
Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-9
MicroVAX and VAX 4000 Model 300 as Systems Dual Hosts
with Shared Expander. . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 2-10

Tables
1-1
1-2
1-3
1-4
1-5

KFQSA Suffixes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
System Software Licenses. . . . . . . . . . . . . . . . . . . . . . . . . . .
MicroVAX Systems With Internal DSSI Adapter. . . . . . . . . .
MicroVAX Systems Without Internal DSSI Adapter .......
VMS Versions, Adapters, and Restrictions. . . . . . . . . . . . . . .

1-4
1-5
1-5
1-5
1-6

Preface
This manual describes the basic MicroVAX dual-host configurations
supported by VAXNMS version 5.3-2.
For information on how to install or operate your dual-host system, see the
Operation or Installation manual for the appropriate MicroVAX system.

Intended Audience
This manual is intended for use by Digital customers who are familiar
with the individual MicroVAX systems that combine into dual-host
configurations.
The content of this manual is primarily reference
information needed to plan configurations of dual-host systems.

Organization
This manual has two chapters, as follow:
Chapter 1 presents an overview of dual hosting and the basic requirements
for dual-host configurations.
Chapter 2 gives examples of supported configurations, with diagrams.

Conventions
The following conventions are used in this manual:
Convention

Meaning

NOTE

Provides general information about the current topic.

CAUTION

Provides information to prevent damage to equipment or software.

WARNING

Provides information to prevent personal injury.

Chapter 1

Dual-Host Systems and DSSI
1.1 Introduction to Dual-Host Systems
A dual-host configuration is made up of two Q-bus MicroVAX systems
connected by a Digital Storage Systems Interconnect (DSSI) bus. The two
systems share one another's Integrated Storage Elements (ISEs) across this
bus. The ISEs can be located within each host, within an expander, or both.
In a dual-host configuration, both systems remain functionally independent.
However, the common DSSI storage bus, together with VAXcluster
software, creates a unique subsystem that makes all media devices
available to both host systems. This provides two data paths for access
to all ISEs by either host.
A dual-host system always includes RF-series ISEs, Ethernet, a DSSI
storage bus, the VMS operating system, and DECnet and VAXcluster
software. A MicroVAX system can also function as dual host with a VAX
4000 series system.

1.1.1 Higher Disk Availability
Dual-host systems provide higher disk availability for critical applications.
A dual-host system can provide automatic failover when used as a server for
satellites in a VAXcluster system. In this instance, the application runs on
the satellite. As such, the dual-host system increases your ability to access
data by providing alternate an access path to the running application if one
of the host systems fails. The user sees a pause in the application. Then,
following the cluster state transition, the application resumes on the other
host with no user intervention.
When an application is running on one of the dual hosts, and that host
system fails, the user has to restart the application on the second host
system.

Dual-Host Systems and DSSI

1-1

1.1.2 Minimized Downtime
In a timesharing environment, a dual-host system minimizes downtime. If
one host fails, a user on that host simply logs in to the second host and
restarts the job, or does an edit/recover routine. The second host in the
configuration assumes responsibility for the application and lets the user
access data on the storage devices connected to the DSSI storage bus. (The
same recovery/restart routine is used in CI VAXclusters.)
Using a dual-host system for a boot server can help eliminate the risk of
cluster downtime if a single host cannot be booted. Dual hosts create two
paths to disk storage, ensuring that the VAXcluster users have automatic
failover to another system if one of the boot servers fails. A dual-host
configuration provides high system and data availability, and maintains
the VAXcluster.
Other advantages of a dual-host configuration include the following:
•

Automatic failover when an application is running on the satellite node

•

Higher availability to data for satellites and timesharing users

•

Read/write file sharing down to the record level

•

Resource sharing through distributed batch and print queues

•

Data and resource sharing through a distributed file system

•

Centralized system management and security

•

Ability to run any VMS application

•

Growth path from a single VAX 4000 or MicroVAX system

•

Greater performance and more I/O than with a single-host system

1.2 Dual-Host Components
Basic dual-host components are the RF-series ISEs, the storage expander,
and the DSSI cable.

1.2.1 RF-Series Integrated Storage Elements
RF -series ISEs are:
RF30 (150 Mbytes)
RF31 (380 Mbytes)
RF71 (400 Mbytes)

1-2 MicroVAX Dual-Host Systems

The ISE has a disk controller on board the physical drive. The ISE
receives a complete packet of information requesting a task to be done. The
intelligent on-board controller interprets the packet and performs the task
without any further communication from other DSSI nodes. At this point,
the ISE begins doing the intelligent tasks of reading, writing, collecting
status, and so forth.
The intelligence of the ISE extends beyond reading and writing. The
intelligent on-board controller can provide detailed status of the ISE, or
start and monitor an internal diagnostic of the ISE.

1.2.2 Supported Expanders
Dual-host systems can be expanded by means of separate enclosures that
contain ISEs. The B213F, R215F, and R400X enclosures expand the DSSI
bus with additional ISEs, with the following specifications for use in a dualhost configuration:
•

One expander per DSSI bus

•

Can be used with systems not based on DSSI by adding KFQSA

1.2.3 External DSSI Cables
One external DSSI cable is required for each connection between systems;
two cables are required to connect two systems and an expander.
External cables connect DSSI storage devices and adapters. The DSSI
external cable, part number BC21M-09, is included with a factoryconfigured dual-host configuration, as well as with expansion boxes. If
your system was not factory-configured, you must order additional cables
separately.

1.3 DSSI Storage Bus and Adapters
Each DSSI storage bus consists of a maximum of eight nodes, two of which
may be adapters and six of which may be ISEs.
Embedded DSSI adapters (EDAs) are the interface between a CPU host and
the DSSI storage bus, connecting the CPU and the intelligent controllers
within each ISE. Once the initialization and device configurations are
complete, the DSSI adapter becomes a passive protocol interpreter, leaving
the communications control to the host CPU and the intelligent controller
on each ISE.
Two basic DSSI adapter designs are in use for dual-host configurations: the
EDA and the KFQSA.

Dual-Host Systems and DSSI

1-3

1.3.1 Embedded DSSI Adapter
The primary adapter design involves DSSI interface logic embedded on the
CPU module. This design is the called the Embedded DSSI Adapter (EDA).

An EDA may be exist along with a KFQSA module in the same host.

1.3.2 KFQSA
The KFQSA is a standard Q-bus option module that may be added to a
MicroVAX system to increase the number of DSSI storage busses connected
to that system. See Table 1-1 for an explanation ofKFQSA suffixes. Each
KFQSA module adds one additional DSSI storage bus to the system.

Table 1-1: KFQSA Suffixes
Suffix

Description

Where Needed

-SA

KFQSA Q-bus to DSSI adapter, factory
installed in BA213 enclosure

For MicroVAX 3800 only; cannot be
ordered separately

-SE

Second KFQSA Q-bus to DSSI adapter,
factory installed in BA2131BA215 enclosure

When new MicroVAX 3300, 3400, or
3800 needs second DSSI adapter

-SG

KFQSA adapter, field installed in
BA2131BA215 enclosure

For existing MicroVAX 3600 or 3900 that
requires its first DSSI adapter, or for
existing MicroVAX 3300, 3400, or 3800
that requires second DSSI adapter

-AA

KFQSA Q-bus to DSSI adapter, field
installed in BA23 or H9642 enclosure

For existing MicroVAX II in BA23
or H9642 cabinet that requires DSSI
adapter

-BA

KFQSA Q-bus to DSSI adapter, field
installed into BA123 enclosure

For existing MicroVAX II in BA123
enclosure that requires DSSI adapter

1.3.3 Embedded DSSI Adapter (EDA)
The other adapter design involves DSSI interface logic embedded on the
CPU module. This design strategy is called the Embedded DSSI Adapter
(EDA). Currently the MicroVAX EDA is found on the KA640 CPU module
(MicroVAX 3300/3400).

An EDA may be installed along with a KFQSA module in the same host,

1-4 MicroVAX Dual-Host Systems

1.4 Configuration Rules for Dual-Host Systems
The following elements are required when planning dual-host configurations.
1. Two Q-bus MicroVAX systems, or one Q-bus MicroVAX and one VAX
4000.
2. Software licenses shown in Table 1-2.

3. DSSI adapters (KFQSA module and/or embedded adapters).
Table 1-3 and Table 1-4.
.

See

4. Ethernet hardware.
5. Maximum of six RF-series ISEs between DSSI adapters.
6. Maximum of four enclosures (two systems, two expanders) per DSSI
storage bus.

Table 1-2: System Software Licenses
First System

. Second System

VMS

VAXcluster

DECnet full-function

DECnet end-node

Table 1-3: MlcroVAX Systems With Internal DSSI Adapter
System

Adapter Type

MicroVAX 3300

Embedded on CPU (EDA)

MicroVAX 3400

Embedded on CPU (EDA)

MicroVAX 3800

KFQSA module

Table 1-4: MicroVAX Systems Without Internal DSSI Adapter·
System

Adapter Requirements

MicroVAXII

KFQSA-AA or KFQSA-BA

MicroVAX 3500

KFQSA-SG

MicroVAX 3600

KFQSA-SG

MicroVAX 3900

KFQSA-SG

Dual-Host Systems and DSSI

1-5

Chapter 2 shows different ways to use MicroVAX systems in dual-host
configurations. As you see in Chapter 2, previously purchased Q-bus
MicroVAX systems can be upgraded to dual-host configurations.

1.5 VMS and Dual-Host Configurations
Table 1-5 shows the VMS versions required to use adapters in the various
dual-host configurations.

Table 1-5: VMS Versions, Adapters, and Restrictions
VMS
Version

Awzter

Adapter

Mo ule

Restrictions

5.0-2A

EDA-to-EDA

EDA6400nly

5.1

EDA640-to-EDA640

No EDAwith KFQSA
Single adapter/system

5.1-1

KFQSA-to-KFQSA

No EDA with KFQSA
Single adapter/system

5.3

Either or both

Mixed adapters allowed
Dual DSSIIdual host allowed

Software requirements also include DECnet and VAXcluster software.

1.6 Module Order
The order of modules for individual. systems in a dual-host configuration
is the same as for single-host configurations. In the case of two KFQSAs
in the same configuration, KFQSA modules are installed at the end of the
respective backplane.

1.7 System Disk
A dual-host configuration may be run using one system disk. Since fewer
failures are seen in expanders than in systems, it is recommended that,
when possible, the system disk be located in an expander.

1-6 MicroVAX Dual-Host Systems

Chapter 2

Supported MicroVAX Dual-Host
Configurations
This chapter contains diagrams illustrating nine supported MicroVAX dualhost configurations.
•

Figure 2-1: MicroVAX hosts, each using a KFQSA adapter

•

Figure 2-2: MicroVAX hosts, each using an EDA adapter

•

Figure 2-3: MicroVAX hosts using mixed adapters

•

Figure 2-4: MicroVAX hosts with EDAs and a shared expander

•

Figure 2--5: Two Q-bus MicroVAX systems with KFQSA adapters and
shared expander

•

Figure 2-6: Two Q-bus MicroVAX systems with a shared expander and
mixed adapters .

•

Figure 2-7: Two non-DSSI MicroVAX systems with two DSSI expanders

•

Figure 2-8: Two Q-bus MicroVAX systems in a dual DSSIIdual-host
configuration

•

Figure 2-9: MicroVAX and VAX 4000 systems as dual hosts with shared
expander

Supported MicroVAX Dual-Host Configurations

2-1

Figure 2-1: Two Q..Bus MicroVAX Systems, Each Using a KFQSA
Adapter

MicroVAX 3800

MLO-004175

In Figure 2-1, ISEs are located in the system enclosures_ You can create
this co:rifiguration with any combination of MicroVAX 3300,3400, and 3800
systems, all of which include internal DSSI storage.

2-2 MicroVAX Dual-Host Systems

Figure 2-2: Two Q-Bus MicroVAX Systems, Each Using an EDA Adapter

MicrcNAX 3400

MicroVAX 3400
TK70

MLO-004176

The configuration in Figure 2-2 can be created with any combination of
MicroVAX 3300 or 3400 systems, which include internal DSSI storage.

Supported MicroVAX Dual~Host Configurations

2-3

Figure 2-3: Two Q-Bus MicroVAX Systems Using Mixed Adapters
MicroVAX 3400

MicroVAX 3800

MLO-O04177

NOTE: VMS V5.3 or later is required for all mixed-adapter configurations.
The configuration in Figure 2--3 can be created with a MicroVAX 3300 or
3400 system combined with a MicroVAX 3800 system, all of which include
internal DSSI storage.

2-4 MicroVAX Dual-Host Systems

Figure 2-4: Two Q-Bus MicroVAX Systems with EDAs and a Shared
Expander
MicroVAX 3300

R215F

MicroVAX 3300

DSSI
\

~--~

~----~~

DSSI
MLO-o04178
"

In Figure 2-4, the two MicroVAX systems share an expander. This
increases the level of availability for dual-host systems with internal nSSI
devices by placing the system and critical data disks in the expander, which
has a separate power supply. The ISEs in the expander are available to all
users on both dual-host nodes if one of the MicroVAX systems is unavailable.

Supported MicroVAX Dual-Host Configurations

2-5

· Figure 2-5: TwoQ-Bus MicroVAX Systems with KFQSA Adapters and
Shared Expander
Non-DSSI MicroVAX
with KFQSA

I-00I._ _ _ _ _...1

R215F

MicroVAX 3800

DSSI '--_ _..I
MLQ.:004179

Figure 2-5 shows a configuration that increases the level of availability for
dual-host systems with internal nSSI devices by placing the system and
critical data disks in the expander, which has a separate power supply.
The ISEs in the expander can continue to operate if one of the Mi(jl'OVAX
systems is unavailable.
This configuration also provides a way to create a dual-host system using
MicroVAX systems that do not have internal nSSI storage, including
MicroVAX II, 3500, 3600, and 3900 systems. These systems can share
nSSI storage when you add a KFQSA storage adapter and place the ISEs
in an expander. Refer to Table 1-4 for applicable KFQSA order names.

2-6 MicroVAX Dual-Host Systems

Figure 2-6: Two Q-BuS MlcroVAX Systems with a Shared Expander and
Mixed Adapters
Non-DSSI MicroVAX II
in a BA23 Box

R215F

MicroVAX 3400

..
~~__~

DSSI ~____~
MLO-004180

NOTE: VMS V5.3 or later is required for all mixed-adapter configurations.

Figure 2--6 shows Q-bus MicroVAX systems, with mixed adapters, sharing
the Same expander.
This configuration increases the level of availability for dual-host systems
with internal DSSI devices by placing the system and critical data disks in
the expander, which has a separate power supply. The ISEs in the expander
can continue to operate if one of the MicroVAX systems is unavailable.
This configuration also provides a way to create a dual-host system using
MicroVAX systems that do not have internal DSSI storage, including
MicroVAX II, 3500, 3600, and 3900 systems. These systems can share
DSSI storage when you add a KFQSA storage adapter and place the ISEs
in an expander. Refer to Table 1-4 for applicable KFQSA order names.
All internal disks (RD54, RA70, and/or RA90) remain local to the system
in which they reside.

Supported MicroVAX Dual-Host Configurations

2-7

Figure 2-7:

Two Non-DSSI MicroVAX Systems with Two DSSI Expanders
R215F

MicroVAX 3900
RA90

R215F

MicroVAX 3900
RA90

RA90

IRA70 RA70J

(!l

1I1
w

eli0

I
I
\

l<:

......

DSSI

DSSI
MLO-0041S1

Figure 2-7 shows a dual-host MicroVAX system that is sharing two
expanders. With ISEs in the expanders, all ISEs are powered up and
available even if one of the MicroVAX systems becomes unavailable.
Any mix of MicroVAX II, MicroVAX 3300/3400, 3500/3600, or 3800/3900
systems may be used.
All internal disks (RD54, RA70, and/or RA90) remain local to the system
in which they reside.

2-8 MicroVAX Dual-Host Systems

Figure 2-8:

Two Q-Bus MicroVAX Systems in a Dual-DSSI, Dual-Host
Configuration
DSSI

DSSI

DSSI
MLO-004182

NOTE: VMS V5.3 or later is required for all mixed-adapter configurations.

In Figure 2-8, the six ISEs within the host enclosures are shared on the
internal (EDA) DSSI bus. The six ISEs in the expanders are shared on the
KFQSA-based bus.

Supported MicroVAX Dual-Host Configurations

2-9

Figure 2-9:

MicroVAX and VAX 4000 Model 300 as Systems Dual Hosts
with Shared Expander
R400X

VAX 4000
TK70

RFxx RFxx RFxx RFxx

MicroVAX 3800
TK70

RFxx

MLO-0041B4

In Figure 2-9, a DSSI-based MicroVAX shares a DSSI bus with a VAX
4000 Model 300 system. The MicroVAX host in this configuration, being
factory-configured, contains one ISE.

2-10

MicroVAX Dual-Host Systems

Appendix A

Related Documentation
The following documents contain information related to the concepts and
hardware maintenance of dual-host system configurations.
Document Title

Order Number

KFQSA Installation and User Guide
RF71 User Guide

EK-KFQSA-IN
EK-RF71E-UG