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Document:	VAX 4000 Dual-Host Systems
Order Number:	EK-390AB-DH
Revision:	2
Pages:	35
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VAX 4000

Dual-Host Systems

Order Number: EK-390AB-DH-002

VAX 4000
Dual-Host Systems

Order Number EK-390AB-DH-002

Digital Equipment Corporation
Maynard, Massachusetts

First Printing, March 1990
Second 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 elTors 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)(l)(ii) of the Rights in Technical Data and Computer
Software clause at DFARS 252.227-7013.
© Digital Equipment Corporation 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

UNmUS
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
COlTect the interference.
S1581

This document was prepared using VAX DOCUMENT, Version 1.2.

Contents
Preface

Chapter 1 Dual-Host Systems and DSSI
Introduction to Dual-Host Systems ................... .
1.1
Higher Disk Availability ......................... .
1.1.1
Minimized Downtime ............................ .
1.1.2
Dual-Host Components ............................ .
1.2
RF-Series Integrated Storage Elements .............. .
1.2.1
1.2.2
R400X Expander .................... '.' ......... .
External DSSI Cables ........................... .
1.2.3
DSSI Storage Bus and Adapters ..................... .
1.3
Embedded DSSI Adapter ......................... .
1.3.1
I(F'QSA ....................................... .
1.3.2
Configuration Rules for Dual-Host Systems ............. .
1.4
Sample Configurations ............................. .
1.5
Software
Levels and Dual-Host Configurations .......... .
1.6
1.7 Module Order .................................... .
1.8 System Disk ..................................... .

Chapter 2
Appendix A

1-1
1-1

1-2
1-2
1-2
1-3
1-3
1-3

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

Supported VAX 4000 Dual-Host Configurations
Related Documentation

Index

III

Figures
2-1
2-2
2-3
2-4

Dual VAX 4000 Model 200 (BA430) Hosts. . . . . . . . . . . . . . .
Dual VAX 4000 Model 300 (BA440) as Dual DSSIlDual Hosts
Dual VAX 4000 Model 200 (BA215) Hosts. . . . . . . . . . . . . . .
Dual VAX 4000 Hosts Model 200 (BA215) and Either Model
200 (BA430) or Model 300 (BA440) .............. . . . . ..
2-5 Dual VAX 4000 Model 200 (BA430) Hosts Sharing an
Expander . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2-6 Dual VAX 4000 Model 200 (BA215) Hosts Sharing an
Expander ............ '. . . . . . . . . .. . . . . . . . . . . . . . . . . .
2-7 Dual VAX 4000 Model 300 (BA440) as Dual DSSIIDual Hosts
Sharing an Expander. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2-8 Dual VAX 4000 Model 300 (BA440) as Dual DSSIlDual Hosts
Sharing Two Expanders. . . . . . . . . . . . . . . . . . . . . . . . . . . ..
2-9 VAX 4000 Model 300 (BA440) and MicroVAX 3800 Hosts
Sharing an Expander. . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..
2-10 VAX 4000 Model 200 (BA215) and MicroVAX 3800 Dual Hosts
2-11 VAX 4000 Model 200 (BA215) and MicroVAX 3300/3400 Dual
Hosts ...........................................

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

2-7
2--8

2-9
2-10
2-11
2-12
2-13

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

KFQSA Suffixes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
System Software Licenses. . . . . . . . . . . . . . . . . . . . . . . . . . .
VAX 4000 and MicroVAX Systems With Internal DSSI . . . ..
MicroVAX Systems Without Internal DSSI ..............
VMS Versions, Adapters, and Restrictions. . . . . . . . . . . . . . .
VAX 4000 Enclosures and Their DSSI Capabilities. . . . . . . .

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

Preface
Thls manual describes the VAX 4000 series dual-host configurations
supported by VAXNMS version 5.3-2 or later.
For information on how to install or operate your dual-host system, see
your system Operation or Installation manuals.

Intended Audience
Thls guide is intended for use by Digital customers who are familiar with
the individual VAX 4000 systems that form dual-host configurations. The
content of thls manual is primarily reference informat.ion needed to plan
configurations of dual-host systems.

Organization
Thls guide has two chapters, as follows:
Chapter 1 presents an overview of dual hosts and the basic requirements
for dual-host configurations.
Chapter 2 gives examples of supported configurations, with diagrams.

Conventions
The following conventions are used in thls manual:
Convention

Meaning

NOTE

Provides general information about the current topic.

CAUTION

Provides information to prevent damage to equipment or software.

WARNlNG

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 VAX 4000 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 VAX 4000 system can also function as dual host with a Qbus MicroVAX 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 edi tlrecover 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 fail over 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 110 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 VAX 4000

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 R400X Expander
The R400X expander provides a VAX 4000 system with additional ISEs.
This DSSI expander has the following specifications for use in a dual-host
configuration:
•

One expander per DSSI bus

•

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

•

Holds up to seven ISEs

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).
A KFQSA module may be installed in a system that contains an EDA.

1.3.2 KFQSA
The KFQSA is a standard Q-bus option module that may be added to a
VAX 4000 system to increase the number of DSSI storage busses connected
to that system. See Table 1-1 for an explanation of KFQSA suffixes. Each
KFQSA module adds one additional DSSI storage bus to the system.
When linked to a MicroVAXin a dual-host configuration, the VAX 4000 may
have as its co-host a system that uses a KFQSA module.

Table 1-1: KFQSA Suffixes
Suffix Description

Where Needed

-SA

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

For MicroVAX 3800 only;
ordered separately

-SE

Additional KFQSA Q-bus to nSSI
adapter, factory installed

When new MicroVAX 3300, 3400, or 3800
needs second nSSI adapter, or when VAX
4000 needs additional nSSI adapter

-SG

KFQSA adapter, field installed

For existing MicroVAX 3600 or 3900 that
requires its first nSSI adapter, or for
existing MicroVAX 3300, 3400, or 3800
that requires second nSSI adapter, or VAX
4000 needing additional nSSI adapter

-AA

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

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

-BA

KFQSA Q-bus to nSSI adapter, field
installed in BA123 enclosure

For existing MicroVAX IT in BA123
enclosure that requires nSSI adapter

cannot be

1.4 Configuration Rules for Dual-Host Systems
The following rules are required for a dual-host configuration:
1. Two VAX 4000 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.

1-4 VAX 4000

Dual-Host Systems

See

4. Ethernet hardware.
5. Maximum of six ISEs on each DSSI bus.
6. Maximum of two system enclosures and one expander per DSSI storage
bus.

Table 1-2: System Software Licenses
First System

Second System

VMS

VAXcluster

DECnet full-function

DECnet end-node

All systems used in dual-host configurations must have DSSI storage
adapters, whether they are embedded on the system module or connected
to the Q-bus by means of a KFQSA module. Table 1-3 and Table 1-4 show
what type of adapter each system uses.

Table 1-3: VAX 4000 and MicroVAX Systems With Internal DSSI
System

Adapter

VAX 4000 Model 300

EDA (2)

VAX 4000 Model 200

EDA (1)

MicroVAX 3300

EDA

MicroVAX 3400

EDA

MicroVAX 3800

KFQSA

Table 1-4: MicroVAX Systems Without Internal DSSI
System

Adapter Requirements

MicroVAX II

KFQSA-AAMKFQSA-BA

MicroVAX 3500

KFQSA-SG

MicroVAX 3600

KFQSA-SG

MicroVAX 3900

KFQSA-SG

Dual-Host Systems and DSSI

1-5

1.5 Sample Configurations
Chapter 2 shows different ways to use VAX 4000 systems in dual-host
configurations. As shown in Figure 2-9 and other diagrams, previously
purchased MicroVAX systems can be upgraded to dual-host configurations
with VAX. 4000 systems.

1.6 Software Levels and Dual-Host Configurations
As shown in Table 1-5, you must have VMS version 5.3-2 or greater to use
VAX 4000 systems in dual-host configurations.

Software requirements also include DECnet and VAX.cluster software.

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

EDA in Systems
or KFQSA

Adapter
Restrictions

5.3-2
or later

VAX 4000 to VAX 4000
VAX 4000 to MicroVAX 3300

Mixed adapters allowed
Dual DSSYdual host allowed

/3400

VAX 4000 to KFQSA

1.7 Module Order
The order of modules for individual systems in a dual-host configuration is
the same as for single-host configurations.

1.8 System Disk
A dual-host configuration may be run using one system disk. Since
expanders fail less often than systems, Digital recommends that, when
possible, you locate the system disk in an expander.

1-6 VAX. 4000

Dual-Host Systems

Chapter 2

Supported VAX 4000 Dual-Host
Configurations
This chapter contains diagrams illustrating eleven supported VAX 4000
dual-host configurations. The configurations are captioned to indicate the
enclosures shown: BA440, BA430, or BA215.

Table 2-1: VAX 4000 Enclosures and Their DSSI Capabilities
Enclosure

VAX 4000
Model

Embedded
nSSI Busses

KFQSA
Slots

BA440

300

BA430

200

BA215

200

The diagrams in this chapter are as follows:
•

Figure 2-1: Dual VAX 4000 Model 200 (BA430) hosts

•

Figure 2-2: Dual VAX 4000 Model 300 (BA440) as dual DSSIIdual hosts

•

Figure 2-3: Dual VAX 4000 Model 200 (BA215) hosts

•

Figure 2-4: Dual VAX 4000 Model 200 (BA215) hosts and either Model
200 (BA430) or Model 300 (BA440))

•

Figure 2--5: Dual VAX 4000 Model 200 (BA430) hosts sharing an
expander

•

Figure 2-6: Dual VAX 4000 Model 200 (BA215) hosts sharing an
expander

•

Figure 2-7: Dual VAX 4000 Model 300 (BA440) as dual DSSIIdual hosts
sharing an expander

•

Figure 2-8: Dual VAX 4000 Model 300 (BA440) as dual DSSIIdual hosts
sharing two expanders

Supported VAX 4000 Dual-Host Configurations

2-1

•

Figure 2-9: VAX. 4000 Model 300 (BA440) and MicroVAX 3800 sharing
an expander

•

Figure 2-10: VAX 4000 Model 200 (BA215) and MicroVAX 3800 dual
hosts

•

Figure 2-11: VAX 4000 Model 200 (BA215) and MicroVAX 3300/3400
dual hosts

2-2

VAX. 4000

Dual-Host Systems

Figure 2-1:

Dual VAX 4000 Model 200 (BA430) Hosts

VAX 4000(BA4xx)
Host A

VAX 4000(BA4xx)
Host B

MLO-004185

In Figure 2-1, ISEs are located in the system enclosures.
The embedded DSSI bus is used by each host to share the six internal ISEs.

Supported VAX 4000 Dual-Host Configurations

2-3

Figure 2-2:

Dual VAX 4000 Model 300 (BA440) as Dual DSSl/Dual Hosts

VAX 4000(BA440)
Host A

VAX 4000(BA440)
Host B

::::>
D...

()

MLO-005671

In Figure 2-2, one DSSI bus (cable running from far left of Host A to far
left of Host B) shares the ISEs installed on the two systems. The other
DSSI bus can be used for communications.

2-4 VAX 4000

Dual-Host Systems

Figure 2-3:

Dual VAX 4000 Model 200 (BA215) Hosts

VAX 4000 (BA215)

VAX 4000(BA215)

MLO-005672

In Figure 2-3, two VAX 4000 Model 200 (BA215) hosts share their two
ISEs.

Supported VAX. 4000 Dual-Host Configurations

2-5

Figure 2-4:

Dual VAX 4000 Hosts Model 200 (BA215) and Either Model
200 (BA430) or Model 300 (BA440)

VAX 4000 (BA21S)

VAX 4000 (BA4xx)

::>
0...

()

DSSI
MLO-005673

In Figure 2-4, a BA215 anc! a BA4xx share four ISEs.

2-6 VAX 4000

Dual-Host Systems

Figure 2-5:

Dual VAX 4000 Model 200 (BA430) Hosts Sharing an
Expander

\' AX 4000(BA430)

VAX 4000(BA430)
R400X

Host A

RFxx RFxx

RFxx

Host B
RFxx

RFxx RFxx

::>

()

0....

MLO-004186

In Figure 2-5, two BA430s share the six ISEs in the expander.

Supported VAX 4000 Dual-Host Configurations

2-7

Figure 2-6:

Dual VAX 4000 Model 200 (BA215) Hosts Sharing an
Expander

VAX 4000(BA21S)

R400X
RFxx

RFxx

::>
0..

()

MLO-005675

In Figure 2-6, two VAX 4000 Model 200 (BA215) hosts share an expander
that contains all the ISEs.

2-8

VAX 4000

Dual-Host Systems

Figure 2-7:

Dual VAX 4000 Model 300 (BA440) as Dual DSSl/Dual Hosts
Sharing an Expander

VAX 4000(BA440)

VAX 4000(BA440)
R400X

Host A

Host B

RFx.x RFx.x RFx.x RFxx

RFx.x RFx.x

I;:,
Q..

()

DSSI

DSSI
MLO·004187

In Figw-e 2-7, the two BA440s share their combined system ISEs on one
of the embedded DSSI busses; they share the ISEs in the expanrer on the
other embedded DSSI bus.

Supported VAX 4000 Dual-Host Configurations

2-9

Figure 2-8:

Dual VAX 4000 Model 300 (BA440) as Dual DSSl/Dual Hosts
Sharing Two Expanders
R400X
RFxx

RFxx RFxx

RFxx

RFxx RFxx

VAX 4000(BA440)
Host A

VAX 4000(BA440)
Host B

RFxx

MLO-004188

In Figure 2-8, the two BA440s are connected by means of each of the two
embedded DSSI busses to a separate, shared expander.

2-10

VAX 4000

Dual-Host Systems

Figure 2-9:

VAX 4000 Model 300 (BA440) and MicroVAX 3800 Hosts
Sharing an Expander
R400X

VAX 4000(BA440)
RFxx

RFxx

MicroVAX 3800
RFxx

RFxx

::::>
c..

DSSI
MLO·004184

Figure 2-9 illustrates the VAX 4000 Model 300 (BA440) as a dual host with
a MicroVAX 3800. The KFQSA module in the MicroVAX 3800 interfaces to
the DSSI storage bus, allowing it to share the ISEs in the exp"ander. The
VAX 4000 interfaces to the DSSI storage bus by means of an embedded
DSSI adapter.
The three RF-series ISEs in the BA440 enclosure are not dual-hosted but
they are available by means of the cluster server.
The MicroVAX host in this configuration is factory configured and contains
one ISE.

Supported VAX 4000 Dt!al-Host Configurations

2-11

Figure 2-10:

VAX 4000 Model 200 (BA215) and MicroVAX 3800 Dual
Hosts

VAX 4000(BA215)

MicroVAX 3800

I I

RFxx TK70

RFxx

I I I

RFxx RFxx TK70

<:
~
<:

::>
~

()

C/)

"u..
~

DSSI
MLO·005676

Figure 2-10 illustrates a dual-host configuration that includes a VAX 4000
Model 200 (BA215) and a MicroVAX 3800 with a total of four ISEs, all
internal to the hosts.

2-12 VAX 4000

Dual-Host Systems

Figure 2-11:

VAX 4000 Model 200 (BA215) and MicroVAX 3300/3400 Dual
Hosts

VAX 4000(BA215)

MicroVAX 3300/3400

D-

MLO-005677

In Figure 2-11, a VAX 4000 Model 200 (BA215) combines with a MicroVAX
3300/3400 to share the two ISEs within the two systems.

Supported VAX 4000 Dual-Host Configurations

2-13

Appendix A

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

Order Number

KFQSA Installation and V ser Guide
RF71 Vser Guide

EK-KFQSA-IN
EK-RF71E-VG