Page 1¶

DISK MIRRORING MODULE¶

ND 210855¶

graph TD;
    System_Disk --> DC1;
    System_Disk --> DC2;
    System_Disk --> DC3;
    DC1 --> A1;
    DC2 --> A2;
    DC3 --> A3;

    classDef disk fill:#f9f,stroke:#333,stroke-width:2px;

    A1[Primary]:::disk;
    A2[Secondary - 1]:::disk;
    A3[Secondary - 2]:::disk;

    Disk_Cluster --> A1;
    Disk_Cluster --> A2;
    Disk_Cluster --> A3;

    subgraph "Disk cluster"
        A1;
        A2;
        A3;
    end;

    note1[DC = Disk Controller] --> System_Disk;

Norsk Data¶

[Photo: Norsk Data logo]

Page 2¶

Disk Mirroring Module¶

Introduction¶

Norsk Data's Disk Mirroring Module secures all data stored on disks, by enforcing that all modifications to the data are written to at least two different disks (mirror disks). Should one disk later fail to operate, the data will be automatically accessed from the mirror unit. It also allows on-line backup while the system (e.g., the database system) is running. This is crucial to those who are heavily dependent upon a system being "up" at all times, such as in transaction-processing applications like banking and finance, manufacturing, transportation and retail markets.

Features¶

Extra security against disk failures; parallel writing on two or three disks.
On-line backup while the system is running.
Includes a "revive" facility which allows for equalising the disks after failure or backup.
Mirroring of both separate physical disks and separate directories (sub-units) on the same physical disk allowed.
Disk mirroring operations are invisible to application programs and most parts of the operating system.
The system throughput is maintained even though duplicated disk units are used.

Page 3¶

Disk Mirroring Module¶

Product Description¶

The system employs two or three equal-size disk units or directories that are updated simultaneously by system software. There is a "primary" disk, the one that the applications see; and "secondary" disk(s), invisible to the applications and most of the operating system. The disks are configured in a "disk cluster." If one disk drive in a cluster fails, an error message is recorded and the disk drive that failed is automatically "disconnected". The system keeps running without interruption, and the failing drive may be serviced at a convenient time.

All write operations issued to a primary disk in a cluster are also automatically performed on the secondary disk(s) in order to keep them equal. Read operations are normally performed on only one unit. An internal "read distribution flag" may be set to direct reads to various units. If this flag is not set, all reads will go to the primary disk. This minimises disk-head movements in cases where reads are more frequent than writes.

The disk drives are kept as equal as possible. However, they may become unequal due to, for example, a failure of one of them or after a backup operation. In this case, the "revive" facility of the disk mirroring module is used to equalise them again, by copying the primary disk to the secondary disk(s). User applications may keep running while the reviving process is taking place.

The Disk Mirroring module allows for taking backup copies of the data disks while the applications are running. This is done by temporarily disconnecting one of the disks from the disk cluster and copying it onto a magtape or a removable disk pack. The disconnected disk can then be reconnected to the disk cluster and the process of reviving can be done while the system is fully operational (available).

Requirements¶

Two or three disk units/directories (fixed or removable) of the same logical size, connected to the same or two SMD or SCSI-type disk controllers. The former configuration is less advisable due to low disk I/O performance.

SINTRAN III operating system, version K or later.

Page 4¶

Corporate Directory¶

Corporate Headquarters¶

ND Headquarters a/s
P. O. Box 5, Bogerud
N-0610 Oslo 6
Norway
Tel.: +47-2-620700
Telex: 2870 nd n
Telefax: +47-2-62284 (A)
Manufacturer

Norway¶

ND Raffel a/s
P. O. Box 70, Bogerud
N-0610 Oslo 6
Norway
Tel.: 47-2-620700
Telex: 47-2-62281 (A)
Sales office
Spangereid, tel.: 47-3-710000
Forus, tel.: 47-4-589090
Trondheim, tel.: 47-7-91222

ND Comptec¶

ND Comptec a/s
P. O. Box 70, Bogerud
N-0610 Oslo 6
Norway
Tel.: 47-2-620700
Telex: 47-2-62280 (A)

Operations¶

Opf Hetalco a/s
P. O. Box 70, Bogerud
N-0610 Oslo 6
Norway
Tel.: 47-2-620700
Telefax: +47-2-62201 (A)

Sweden¶

ND Norge Data A/B
Kanalbanken AB
S-1169 Upplands Vasby
Sweden
Tel.: +46-8-590070
Telex: 86573 nddata s
Gothenburg, tel.: +46-31-96570
Malmö, tel.: +46-40-70510

ND-Silvidata¶

Sweden
S-890 Sundsvall
Sweden
Tel.: +46-60-151150
Vaxjo, tel.: +46-470-18500

Denmark¶

Norsk Data A/S
Lautrupbæk 1-3
P. O. Box 129
DK-2750 Ballerup
Tel.: +45-8-671244
Telefax: +45-8-66641 (A)
Copenhagen, tel.: +45-2-682100
Aarhus, tel.: +45-861916
Aalborg, tel.: +45-816800

Finland¶

OY Norsk Data A/B
Pultimukentæukouko 2
SF-0071 Helsinki 1
Tel.: +358-0-3661611
Telefax: +358-0-94644 (A)
Sales: +358-0-36942
Oulu, tel.: +358-21-27022

United Kingdom¶

Norsk Data Ltd.
Bermelyn Valence
Rm1 3GF
United Kingdom
Tel.: +44-1-439-3594
Fax: +44-1-396-35964
London, tel.: +44-1-347-8922
Reading, tel.: +44-734-58607
Birmingham, tel.: +44-21-427-5230
Gosforth, tel.: +44-688-96404
Leeds, tel.: +44-531-824150
Herford, tel.: +44-442-592381
Worples: +44-479-305942

West Germany¶

Norsk Data GmbH
Tonnastrasse 10-12
6000 Baf Homburg v.d.H.
West Germany
Tel.: +49-6172-80460

Belgium¶

Wordplex Belgium S.A.
Excelsiorlaan 2
1930 Brussels
Belgium
Tel.: 00-32-7201580
Brussels, tel.: 00-32-7200900
Telefax: 00-32-7210801

France¶

Norsk Data Paris
32 Ave Grange-Dame-Rose
92140 Veluzay-La-Forêt
France
Tel.: +33-1-45037030
Telefax: +33-1-45037060

Ireland¶

Norsk Data Ireland Ltd., A/S
IDA Industrial Estate, Sentry Avenue
Dublin 9
Ireland
Tel.: 353-1-472744
Telefax: 353-1-472868

Luxembourg¶

Wordplex Luxembourg
Rue de l'Industrie No.9
1811 Luxembourg
Tel.: 352-492131

The Netherlands¶

Norsk Data Nederland B.V.
Breyssel 50
3944 AB Nonweigen
The Netherlands
Tel.: 31-340-72811

Spain¶

Norsk Data - Wordplex Espana S.A.
Paseo de Gracia 50
08807 Barcelona
Spain
Tel.: +34-3-2165000
Telefax: +34-3-2485461

Switzerland¶

Norsk Data (Switzerland) S.A.
Chem. du Vivlduc 12
CH-1010 Preutz-Lausanne
Switzerland
Tel.: +41-21-27012

Australia¶

Wordplex Australia Pty. Ltd.
Unit 4, A Sydney Place
Frazertech (Sydney)
New South Wales 2068
Australia
Tel.: +61-2-951-9353

Hong Kong¶

Norsk Data International
Sing Wong Center
111 Connaught Road
Hong Kong
Tel.: 5-852-161365

USA¶

Norsk Data A. Inc.
Ninebrookserk Office Park
Westerport Drive, Suite 150
Westborough
MA 01581
USA
Tel.: 1-617-366-3496
Telefax: +1-617-380036 (A)

Agents and Distributors In¶

France¶

Martec Datasystemes S. A. Paris
Tel.: 33-3-6938580

Iceland¶

Norsk Data Iceland
Sao:o-tel
Tel.: 351-614-9 gwseagy s. erf. nov. 190186

India¶

Norsk Data India Pty. Ltd.
Tel.: 914-1174-1270/910925

[Photo: ND Logo]