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					DuplexWrite 1.0

Biebl, Braun
Siemens Nixdorf Informationssysteme AG Primergy
81730 München
e-mail: Internet:DOCetc@mchp.siemens.de
Tel.: (089) 636-43572
Fax: (0 89) 6 36-4 87 17
U41115-J-Z145-1-76
Sprachen: En




Edition August 1999
Comments… Suggestions… Corrections…
The User Documentation Department would like to know
your opinion on this manual. Your feedback helps us to
optimize our documentation to suit your individual needs.
Fax forms for sending us your comments are included at the
back of the manual.
There you will also find the addresses of the relevant User
Documentation Department




Copyright and Trademarks
Copyright © 1999 Siemens AG.

All rights reserved.
Delivery subject to availability; right of technical modifications reserved.

All hardware and software names used are trademarks of their respective manufacturers.




This manual is printed on
paper treated with
chlorine-free bleach.
Introduction




Installation and configuration




Running DuplexWrite




Configuring DuplexWrite




Background information




Reference section and index
Contents
1         Introduction . . . . . . . . . . . . . . . . .                       .   .   .   .   .   .   .   .   .   .   .   1
1.1       Summary . . . . . . . . . . . . . . . . . .                          .   .   .   .   .   .   .   .   .   .   .   1
1.2       Objectives of this manual . . . . . . . . . .                        .   .   .   .   .   .   .   .   .   .   .   1
1.3       Fonts and symbols used . . . . . . . . . . .                         .   .   .   .   .   .   .   .   .   .   .   2
1.4       User-friendly documentation – verified quality                       .   .   .   .   .   .   .   .   .   .   .   3

2         Installation and configuration           .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .    5
2.1       Software installation . . . . . .        .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .    5
2.1.1     Remote version . . . . . . . .           .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .    5
2.1.2     Standalone version . . . . . .           .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .    5
2.2       Deinstallation . . . . . . . . .         .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .    6

3         Running DuplexWrite . . . . . . . . . . .                            .   .   .   .   .   .   .   .   .   .   .    7
3.1       Remote Version . . . . . . . . . . . . . . .                         .   .   .   .   .   .   .   .   .   .   .    7
3.1.1     Mass Storage: Device View window . . . . .                           .   .   .   .   .   .   .   .   .   .   .    7
3.2       DuplexWrite standalone version . . . . . . .                         .   .   .   .   .   .   .   .   .   .   .    9
3.2.1     The DuplexWrite: Disk List window . . . . .                          .   .   .   .   .   .   .   .   .   .   .    9
3.3       The DuplexWrite: Disk group window . . . .                           .   .   .   .   .   .   .   .   .   .       12
3.4       The Disk Info Dialog . . . . . . . . . . . . .                       .   .   .   .   .   .   .   .   .   .       17
3.5       The DuplexWrite: Config Disk Group window                            .   .   .   .   .   .   .   .   .   .       19
3.6       DuplexWrite status icons . . . . . . . . . .                         .   .   .   .   .   .   .   .   .   .       21

4         Configuring DuplexWrite . . .            .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .       23
4.1       Setting Up a DuplexWrite Disk .          .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .       23
4.2       Handling Disk Errors . . . . . .         .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .       24
4.3       MS Cluster Server Support . .            .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .       26

5         Background Information       .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .       29
5.1       Data Duplexing . . . . .     .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .       29
5.2       Data Recovery . . . . . .    .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .       30
5.3       Registry Entries . . . . .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .       31

Glossary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

Figures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

Tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

Related publications . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45




U41115-J-Z145-1-76
1         Introduction

1.1       Summary
DuplexWrite is a software to improve the availability of disk storage subsystems.
In combination with Fibre Channel connection technology, disaster-tolerant
configurations can be set up. DuplexWrite duplicates write operations so that two
disks of different disk storage subsystems contain identical data. This solution
is a so-called "physical mirroring" because it is independent of any logical data
structures such as file system data.
DuplexWrite can be configured in two ways:
– The standalone version allows local administration of DuplexWrite. The
  configuration dialog can be accessed via the Control Panel Entry
  Duplex Write.
– The remote version is fully integrated into the Siemens ServerView graphical
  user interface. It can be accessed via ServerView's subdialog
  Mass Storage: Device View.


1.2       Objectives of this manual
This manual deals with the standalone and the ServerView integrated versions
of DuplexWrite.
This manual is intended for system administrators who have a working
knowledge of hardware and data transfer.




U41115-J-Z145-1-76                                                              1
Fonts and symbols used                                                  Introduction


1.3        Fonts and symbols used

Italics                    Identifies commands and input in body text

typewriter font            Indicates output from the system and text displayed on
                           the screen

boldface                   Used for emphasis in the body of the text

"Quotation marks"          indicate references to other chapters, sections or
                           manuals

Ê                          Indicates an action you must perform

I                          This symbol is followed by supplementary information,
                           comments and hints.

V                          Pay special attention to text marked with this symbol.
                           Failure to observe such a warning could endanger
                           lifes, destroy the system, or lead to loss of data.

Table 1: Notational conventions




2                                                                 U41115-J-Z145-1-76
Introduction                  User-friendly documentation – verified quality


1.4       User-friendly documentation –
          verified quality
As part of its efforts to further improve the information provided for users, the
editorial department responsible for this manual has been independently
audited to verify its high standards of quality of the documentation.
This audit was carried out by TÜV PRODUCT SERVICE GmbH. The following
aspects were investigated:
–   General comprehensibility
–   User-friendliness
–   Occupational hygiene and safety for the users
–   Safety of the application and observance of the relevant
    regulations, standards and guidelines
–   Environmental protection
–   Layout, realization, readability
–   Conformity with the product
–   Accuracy and completeness of the contents
The criteria for the audit were developed in a joint project between
TÜV PRODUCT SERVICE GmbH and
tekom, Gesellschaft für technische Kommunikation e.V.

                                        The DOCcert seal provides visible
                                        evidence of the successful completion
                                        of the audit.




U41115-J-Z145-1-76                                                                  3
2         Installation and configuration

2.1       Software installation

2.1.1     Remote version

The user interface of the ServerView integrated version is delivered with
ServerView. We recommend you install ServerView prior to DuplexWrite.
When you install ServerView agents you can choose the remote version of
DuplexWrite by checking the appropriate box (see manual “ServerView - Server
Management“, section “Installing ServerView Agents”).


2.1.2     Standalone version

DuplexWrite is delivered on the Siemens Duplex Data Manager-CD-ROM. The
software runs under Windows NT 4.0 and requires Service Pack 5 or higher.
Ê Make sure you have administrator rights.
    I In MSCS configurations, a special cluster service has to be installed.
          This requires cluster administrator rights. User ID and password are
          required!
Ê Insert the Siemens Duplex Data Manager CD-ROM.
Ê Run DuplexWrite.exe from the CD.
Ê Follow the installation instructions.
Ê Reboot the system after completing the installation process.




U41115-J-Z145-1-76                                                           5
Deinstallation                                     Installation and configuration


2.2       Deinstallation
DuplexWrite can be deinstalled using the standard Windows NT procedures.
Ê Select the Add/Remove Software applet in the Control Panel window.
Ê Close the Control Panel window.
    I The DuplexWrite applet cannot be removed while the Control Panel is
          opened or the applet itself is in use!
Ê Select DuplexWrite from the list of software to be removed.
Ê Press the Remove botton.
Ê Reboot the system after completing the deinstallation process.




6                                                             U41115-J-Z145-1-76
3          Running DuplexWrite

3.1        Remote Version
The remote version is fully integrated into the Siemens ServerView graphical
user interface. It can be accessed via ServerView's subdialog
Mass Storage: Device View.


3.1.1      Mass Storage: Device View window

When DuplexWrite is installed, the following items are added to the
Mass Storage: Device View dialog of ServerView:
– Columns: DWrite Status, Duplex Disk
– Botton: DW Configure




Figure 1: Mass Storage: Device View window



U41115-J-Z145-1-76                                                             7
Remote Version                                                Running DuplexWrite


DWrite Status
Entries in the column DWrite Status can have one of the following values:

Value           Meaning
Online          Disk is online, configured for DuplexWrite
Error           disk is offline due to an error condition
Recover         disk is recovering
Disabled        disk has been set inactive due to maintenance activity
Simplex         disk has not been configured for DuplexWrite
N/A             no DuplexWrite provided, or cannot get status
MultiPath       second, third or fourth path to disk via MultiPath
Missing         disk is missing (entry generated by partner disk’s COD; see
                glossary for an explanation of “COD”)
<name>          disk is used by other MSCS cluster node <name>


Duplex Disk
The column Duplex Disk is needed to identfy the DuplexWrite Groups (for more
information, see glossary, “Duplex Write Group“). A DuplexWrite group consists
of one or two disks.

DW Configure
The button DW Configure is used to configure a DuplexWrite group.
The DW Configure button is selectable (not gray), if the DuplexWrite agent on the
selected server is installed and if the selected entry has a DuplexWrite status
other than N/A, MultiPath, or <cluster node name>.
To configure a DuplexWrite group, select an entry in the MassStorage: Device View
menu and click the DW Configure button. This will open the Disk group dialog. For
further information see section “The DuplexWrite: Disk group window” on
page 12.
I All changes in the DuplexWrite configuration dialog instantly (after user
        confirmation) affect the DuplexWrite configuration.




8                                                                U41115-J-Z145-1-76
Running DuplexWrite                            DuplexWrite standalone version


3.2        DuplexWrite standalone version
Since ServerView is network based and uses SNMP a DuplexWrite standalone
version, for security reasons, is provided which does not use SNMP. Instead, the
functionality is available through the Control Panel applet.

          This applet starts the DuplexWrite: Disk List dialog.


I Only users belonging to the Administrator group are permitted to
        configure DuplexWrite.


3.2.1      The DuplexWrite: Disk List window

This dialog lists all disks known to DuplexWrite including some short information.
Detailed information on each disk is available via the DuplexWrite: Disk Group
dialog (see section “The DuplexWrite: Disk group window” on page 12.
I No configuration is possible if no DuplexWrite driver is installed. All entries
        in the list will be marked with DWrite Status N/A or Simplex.




Figure 2: DuplexWrite: Disk List window




U41115-J-Z145-1-76                                                               9
DuplexWrite standalone version                              Running DuplexWrite


Disk List entries
Duplex Disk
      ID of the DuplexWrite group. 'N/A', or '-' if the entry does not belong to a
      DuplexWrite group.
       The disk's current DuplexWrite status is indicated by a status icon (see
       the section “DuplexWrite status icons” on page 21).
DWrite Status
      Entries in the column DWrite Status can have one of the following values:

       Value           Meaning
       Online          Disk is online, configured for DuplexWrite
       Error           disk is offline due to an error condition
       Recover         disk is recovering
       Disabled        disk has been set inactive due to maintenance activity
       Simplex         disk has not been configured for DuplexWrite
       N/A             no DuplexWrite provided, or cannot get status
       MultiPath       second, third or fourth path to disk via MultiPath
       Missing         disk is missing (entry generated by partner disk’s COD;
                       see the glossary for an explanation of “COD”)
       <name>          disk is used by anoother MSCS cluster node <name>


Disk
       Windows NT disk number or 'N/A'.
       I With MultiPath, disks can be listed twice. Disk numbers will only
               be shown for entries which are assigned to the first MultiPath
               channel.
SCSI bus related information:
       Port    port name, e.g. SCSI<x>, where x is the number of the port
       Chn     Channel Identifier
       TID     Target Identifier (SCSI-ID)
       LUN Device Logical Unit (SCSI-LUN)




10                                                                 U41115-J-Z145-1-76
Running DuplexWrite                             DuplexWrite standalone version


Driver Name
       Driver Name for the controller / port.
       I If no DuplexWrite driver is installed all list entries will be marked
              DWrite Status Simplex or N/A.

Disk List buttons
Close Closes the DuplexWrite Disk List dialog
Select Starts the DuplexWrite: Disk Group dialog
Register
      Registers the DuplexWrite driver for the selected disk. Selectable if a disk
      with status N/A is selected. Applicable to a previously unregistered disk
      only.
       I ATAPI drivers are not supported by DuplexWrite.
Unregister
      Unregisters the DuplexWrite driver for the selected disk. An unregistered
      disk is ignored by the DuplexWrite driver and will not be configured. It is
      listed with a status of N/A.
       Selectable if a disk with status Simplex is selected.
       I This option can be used, for example, to speed up the device scan
              on reconfiguration. Unregistered devices will not be investigated
              by DuplexWrite.
Help Starts the Help dialog
V A change of the hardware configuration - e. g. add/remove of a controller
       - may change the NT portnames. The states Register/Unregister and
       Prefer are stored in registry key associated to the portname. Renaming
       the port will destroy this state information, therefore. Check your
       Duplex Write settings when the hardware has been modified!




U41115-J-Z145-1-76                                                             11
The DuplexWrite: Disk group window                         Running DuplexWrite


3.3        The DuplexWrite: Disk group window
In this dialog, a single DuplexWrite Disk group can be configured.
I Detailed disk information is available by double click the desired disk
       entry (see section “The Disk Info Dialog” on page 17).




Figure 3: DuplexWrite: Disk Group window

I ServerView provides the Archive Data Mode for data snapshots and offline
       reading of configuration data. If this mode is enabled, no configuration of
       DuplexWrite is allowed. All buttons and check boxes with the exception of
       the Close, Print, and Help button are disabled.




12                                                              U41115-J-Z145-1-76
Running DuplexWrite                      The DuplexWrite: Disk group window


DuplexWrite Disk group
DWrite Status
      An entry in the column DWrite Status can have one of the following values:

       Online          Disk is online, configured for DuplexWrite
       Error           disk is offline due to an error condition
       Recover         disk is recovering
       Disabled        disk has been set inactive due to maintenance activity
       Simplex         disk has not been configured for DuplexWrite
       N/A             no DuplexWrite provided, or cannot get status
       MultiPath       second, third or fourth path to disk via MultiPath
       Missing         disk is missing (entry generated by partner disk’s COD;
                       see the glossary for an explanation of “COD”)
       <name>          disk is used by another MSCS cluster node <name>


Disk
       Windows NT disk number
       I With MultiPath, disks can be listed twice. Disk numbers will only
               be shown for entries which are assigned to the first MultiPath
               channel.
SCSI bus related information:
       Port    port name, e.g. SCSI<x>, where x is the number of the port
       Chn     Channel Identifier
       TID     Target Identifier (e.g. SCSI-ID)
       LUN Device Logical Unit (e.g. SCSI-LUN)
Driver Name
       Driver Name for the controller / port
       I If no DuplexWrite driver is installed all list entries will be marked
               with DWrite Status Simplex or N/A. Administration is not supported.




U41115-J-Z145-1-76                                                              13
The DuplexWrite: Disk group window                            Running DuplexWrite


Data Field
This data field provides additional information on the selected disk:
Inquiry Data:
       Inquiry string of the device.
Real Size (MB):
      Real size of the disk in Mbytes.
DWrite Size (MB):
      Effective size of the DuplexWrite group in Mbytes.
Reason
     Shows the reason for the selected disk with status Error.

Action on Selected Disk
This group of buttons acts on the selected disk.
Create/Add:
      Creates a DuplexWrite Disk group, if a disk with status Simplex is selected.
      The new status is Online.
         Adds a second disk calling the Config Disk group dialog, if a disk with
         DWrite Status Online is selected. The new status is Error.
         Selectable, if a disk with status Simplex or Online is selected.
         I For a creation (create/add disk) of a DuplexWrite Disk group, a raw
                disk device is needed.
Disable
      Can be used to shut down a disk for maintenance. The new status is
      Disabled.
Prefer
         Sets the disk preference for reading in the DuplexWrite Disk group.
         Selectable (not gray) if both disks of a DuplexWrite Disk group have the
         status Online and the selected disk is not prefered. The color of the check
         mark in the status bitmap of the prefered disk is red.
         I By default, the first disk in the DuplexWrite Disk group is preferred.



14                                                                U41115-J-Z145-1-76
Running DuplexWrite                        The DuplexWrite: Disk group window


Recover/Online
     Selectable if a disk with DWrite Status Error or Disabled is selected.
         The action depends on the state of the selected DuplexWrite group:
         q   The selected DuplexWrite group consists of two disks and
             DWrite Status of partner disk is Online:
             Recover the DuplexWrite group: copy back all data from partner disk.
             After recovering, the new status is Online.
         q   The selected DuplexWrite group consists of two disks and the DWrite
             status of both disks is Error or Disabled:
             Set the status of the selected disk to Online. Subsequently, the
             DuplexWrite group will be accessible to the application.
         q   The selected DuplexWrite group contains only one disk:
             Sets the status of the selected disk to Online.
         q   If the DWrite Status of the selected disk is Missing, a disk matching the
             COD data (same unique ID) will be looked for. If found, the entry will
             change from Missing to Error .
Delete
         Deletes a disk from a DuplexWrite group. The new status is Simplex. No
         user data will be affected. A Missing entry will be deleted entirely.
         Selectable if a disk with DWrite Status Error, Disabled, or Missing is
         selected.
Cancel
     Cancels the recovery process. The new status is Error.
     Selectable, if a disk with status Recover is selected.

Textbox Messages
Shows messages from all DuplexWrite groups from the time the dialog started.
I All DuplexWrite driver events are logged by the standard NT event
         logging. Additionally, current messages are shown within a textbox of the
         DuplexWrite: Disk Group Dialog. In the ServerView integrated version all
         events and traps are recorded by the Alarm Monitor of ServerView.




U41115-J-Z145-1-76                                                                 15
The DuplexWrite: Disk group window                        Running DuplexWrite


Global Buttons
Close Closes the DuplexWrite Disk group dialog
Refresh Refreshes shown Disk group data. Recommended in case of failure
      situations to ensure that status shown is the current one.
      I In some rare cases, a refresh may take up to a few minutes.
Print Prints all DuplexWrite Disk group information. Supported in the ServerView
      integrated version only.
Help Starts Help dialog
V A change of the hardware configuration - e. g. add/remove of a controller
      - may change the NT portnames. The states Register/Unregister and
      Prefer are stored in registry key associated to the portname. Renaming
      the port will destroy this state information, therefore. Check your
      Duplex Write settings when the hardware has been modified!




16                                                            U41115-J-Z145-1-76
Running DuplexWrite                                         The Disk Info Dialog


3.4        The Disk Info Dialog
This dialog provides some additional information on each disk. Information is
read from the disk device directly, or it will be retrieved from the partner disk's
COD data when the actual disk itself is not accessible.
I Due to implementation reasons, the ServerView integrated version does
       not support all fields. Use DuplexWrite's standalone version to get full
       information.
Double click on the desired disk entry in the Disk group Dialog to get the detailed
disk information:




Figure 4: DuplexWrite: Disk Info window




U41115-J-Z145-1-76                                                                17
The Disk Info Dialog                                        Running DuplexWrite


The following information is displayed:
DuplexWrite Disk Group
      the disk's current DuplexWrite Group id (DuplexWrite Disk only)
DuplexWrite Disk Key
      a unique DuplexWrite group key (DuplexWrite Disk only)
Disk Information
      SCSI bus related information:
               Port   port name, e.g. SCSI<x>, where x is the number of the port
               Chn    Channel Identifier
               TID    Target Identifier (e.g. SCSI-ID)
               LUN Device Logical Unit (e.g. SCSI-LUN)
      Host
               computer name where DuplexWrite Disk has been created
      Inquiry Data
             inquiry string of the device
      Real Size
            real size of the disk in Mbytes
      DWrite Size
            the effective size of the DuplexWrite group in Mbytes
      status
               DWrite Status
      <message text>
           detailed status information, e.g. error or fault reason
      Last Update
            the date of last write operation to this disk
      Debug Info
           ...for debugging purposes...




18                                                             U41115-J-Z145-1-76
Running DuplexWrite               The DuplexWrite: Config Disk Group window


3.5        The DuplexWrite:
           Config Disk Group window
This dialog adds the second disk to a DuplexWrite Disk group.
I If Archive Data Mode in ServerView is enabled, this dialog is blocked.




Figure 5: DuplexWrite: Config Disk group window

The dialog window is divided into two parts:
– The upper list box displays the first disk of a DuplexWrite group.
– The lower list box displays all disks with the status Simplex and with a size
  greater than or equal to the first disk of the current DuplexWrite group.




U41115-J-Z145-1-76                                                            19
The DuplexWrite: Config Disk Group window                  Running DuplexWrite


List box entries
Disk
        Windows NT disk number.
SCSI Bus related information:
        Port   port name, e.g. SCSI<x>, where x is the port number
        Chn    Channel identifier
        TID    Target identifier (SCSI-ID)
        LUN Device logical unit (SCSI-LUN)
Size (MB)
       Real size of the disk in Mbytes.
        I The size of the first DuplexWrite Disk (upper list box) is the reduced
               disk size. This size may be smaller than the disk’s real size
               because of previous size adjustments to a smaller DuplexWrite
               Group.
Driver Name
       Driver Name for the controller / port.
Close
        Closes the DuplexWrite Config Disk group dialog.
Add     Adds the selected disk to the DuplexWrite group and closes the
        DuplexWrite: Config Disk group dialog.
Help Starts the Help dialog




20                                                            U41115-J-Z145-1-76
Running DuplexWrite                                     DuplexWrite Status icons


3.6        DuplexWrite Status icons

Icon      DuplexWrite       Remarks
          status
          Online            DuplexWrite Disk, preferred for read


          Online            DuplexWrite Disk, not used for read


          Error             disk is offline due to an error condition


          Recover           disk is recovering


          Disabled          disk has been set inactive due to maintenance activity


          Simplex           disk has not been configured for DuplexWrite


          N/A               no DuplexWrite provided, or cannot get status


          MultiPath         second, third or fourth path to disk via MultiPath


          Missing           disk is missing (entry generated by partner disk's
                            COD)

          <name>            disk is used by another MSCS cluster node <name>


Table 2: DuplexWrite status icons




U41115-J-Z145-1-76                                                               21
4          Configuring DuplexWrite

4.1        Setting Up a DuplexWrite Disk
Each DuplexWrite Disk has to be partitioned into the COD (Configuration On
Disk) data area and the user partitions.
The COD area is a non-standard partition to be used by DuplexWrite. It contains
DuplexWrite configuration and status data as well as information on the partner
disk, the last update, and the host's name.
The COD partition must be the first partition on LUN as shown in the example
below (output of Windisk.exe):




Figure 6: COD partition

To set up a DuplexWrite disk proceed as follows:
Ê Use Windisk.exe to cleanup (both) disks: remove all partitions.
    V All previous disk data will be destroyed!
Ê Use the Disk Group dialog of DuplexWrite to create/add the DuplexWrite
  disks.
Ê Use Windisk.exe to create the user partitions.




U41115-J-Z145-1-76                                                           23
Handling Disk Errors                                    Configuring DuplexWrite


I The current version of DuplexWrite can only handle “clean” disks. Existing
        data must be backed up, and restored once the DuplexWrite Disk has
        been created.
V Don't delete a COD partition using Windisk.exe. This will damage the
        partition table! Delete a COD partition first using the DuplexWrite
        command Delete. This will change the partition type from Unknown to
        Unused.
V Mirroring the system disk needs special handling. Currently, this
        functionality is not released.


4.2         Handling Disk Errors
DuplexWrite disks are maintained by DuplexWrite's Disk Group dialog (see
section “The DuplexWrite: Disk group window” on page 12). Use this dialog to
monitor and change the disks’ status. Detailed disk information is available by
double clicking the disk entry.
The following section describes various error conditions and the recommended
action for the user to take.

Example 1
     One DuplexWrite disk reports an Error status.




     All data can be recovered from the partner disk:
     Ê Select the disk with DWrite status Error and click Recover/Online.




24                                                            U41115-J-Z145-1-76
Configuring DuplexWrite                                   Handling Disk Errors


Example 2
   When the faulty disk (LUN) has been removed it is still known through the
   COD data of the partner disk. It will subsequently be listed as Missing. No
   SCSI related information is available:




   Ê Double click the Missing entry to get the stored COD information
   Before a new disk (LUN) can be added to the current DuplexWrite group the
   Missing entry has to be deleted:
   Ê Select the entry and click Delete.

Example 3
   When both disks show an Error status the DuplexWrite group is not available
   to the application. This situation shows higher operating system levels
   similar to a disk failure. Further reaction depends on the application. Duplex-
   Write ensures that all data written before this double error occurred is safe.




U41115-J-Z145-1-76                                                             25
MS Cluster Server Support                                Configuring DuplexWrite


     Ê Choose the disk with the most recent data for data retrieval. Use Disk Info
       Dialog to get the information on the last update.
     Ê Select the appropriate disk and press Recover/Online. DWrite status
       should change to Online.
     Ê Proceed as described in the first case above (Online/Error).
I In case of MSCS cluster configurations avoid misinterpretation of data
        shown (see section “MS Cluster Server Support” for more information).


4.3        MS Cluster Server Support
The MS Cluster Server (MSCS) provides additional host failure tolerance and
can be combined with DuplexWrite or MultiPath to achieve full disaster tolerance.
Even if DuplexWrite uses a duplexing method which is transparent to the appli-
cation, MSCS requires special handling:
– Disks are shared among cluster nodes. Configuration data and states can
  be changed by another node.
– MSCS uses the special SCSI commands Reserve and Release. A reserve
  command makes a disk inaccessible to other nodes.
DuplexWrite provides a special cluster service to inform the other nodes on
configuration changes. This allows DuplexWrite to maintain additional infor-
mation even when a shared disk currently is assigned to another system.

Example
     The following example demonstrates the effects of SCSI reservation:
     Consider a cluster system composed of two the nodes A and B. The shared
     DuplexWrite disks currently are assigned to node A. Because of the SCSI
     reservation these disks cannot be read by node B. The COD data is invisible
     and the disks appear to node B like defective simplex disks.




26                                                              U41115-J-Z145-1-76
Configuring DuplexWrite                         MS Cluster Server Support


   DuplexWrite group as seen from node A; disk 5 currently recovering:




   The same DuplexWrite group as seen from node B; the disks already known
   to DuplexWrite as configured for MSCS:




   In some rare cases, DuplexWrite does not know of the disk's MSCS configu-
   ration. Both disks will appear like an unreadable simplex disk:




U41115-J-Z145-1-76                                                       27
MS Cluster Server Support                            Configuring DuplexWrite


I If a disk is reserved by another cluster node, only SCSI Bus will be
      available. No configuration data - not even disk sizes - can be shown.
      Use the SCSI bus information for disk identification.




28                                                          U41115-J-Z145-1-76
5         Background Information
DuplexWrite is a software to improve the availability of disk storage subsystems.
In combination with Fibre Channel connection technology, disaster-tolerant con-
figurations can be set up. DuplexWrite duplicates write operations so that two
disks of different disk storage subsystems contain identical data. This solution
is a so-called "physical mirroring" because it is independent of any logical data
structures such as file system data.
If one of the drives fails DuplexWrite ensures that the data can continue to be
processed without interruption by accessing the disk still in service. When the
faulty drive has been repaired, data recovery can be performed online during
normal operations. No reboot is necessary. This applies to physical disks as well
as to complex RAID volumes.
Additional fault tolerance can be achieved using MultiPath which handles redun-
dant Fibre Channel connections. The Duplex Data Manager combines both pro-
ducts MultiPath and DuplexWrite and offers high availability in terms of connec-
tion and storage system failures. In combination with MS Cluster Server a full
disaster-tolerant configuration can be set up.


5.1       Data Duplexing
DuplexWrite duplicates each write operation to both members of a
DuplexWrite Group (see Glossary entry “DuplexWrite Group” on page 36). The
DuplexWrite Group appears to the operating system as one disk. Data is written
to both disks as long as no error condition occurs. As a result, both disks of a
DuplexWrite Group contain identical data. Duplexing is done based on disk
LUNs, including the virtual LUNs of a RAID subsystem.
Data is read from one specified disk, called Preferred Disk. This disk can be sel-
ected from the DuplexWrite Group. In case of an error - up to 3 unsuccessful
retries - the corresponding disk's status is set to Error and the disk subsequently
will not be used any more. The error is logged and a notification is sent to the
user that this disk has been disabled.
Configuration data and DuplexWrite states are stored on disk. DuplexWrite uses
a special, non-standard partition for configuration of disk (COD) storage. User
data remains unchanged and is stored on standard partitions: all (user) data is
mirrored physically.




U41115-J-Z145-1-76                                                              29
Data Recovery                                              Background Information


5.2        Data Recovery
In normal operation, both disks of a DuplexWrite Group contain identical data. In
case of an error or fault, the affected disk's state is set to Error and the disk sub-
sequently will not be used. All data, however, is safe on the remaining partner
disk.
Before a disk can be returned to its DuplexWrite Group, it has to be updated: All
data has to be copied to the disk. This is performed online during regular ope-
ration. If a write operation occurs while data is being recovered DuplexWrite syn-
chronizes the write operation so that a consistent state is guaranteed. When the
recovery process is completed successfully, the disk's state is set to Online,
COD data is updated, and the disk again becomes a fully functional member of
the DuplexWrite Group.




30                                                                U41115-J-Z145-1-76
Background Information                                          Registry Entries


5.3          Registry Entries
DuplexWrite uses registry keys to define preferences. Some of them can be
changed to modify DuplexWrite's behavior.
V Changing registry keys may result in severe system damage. Only
        advanced users should edit the registry.

Registry path:       HKL/System/CurrentControlSet/Services/DuplexWrite/...


relative path:       Parameters/P<port>C<channel>T<target>L<lun>
value type:          DWORD
bit flags:           0x1   EXCLUDE_DISK
                               Don't use this disk for DuplexWrite.
                                  Useful e.g. to speed up the device scan on
                                  reconfiguration. Excluded devices will not be
                                  investigated by DuplexWrite.
                                  This flag is affected by the commands
                                  Register/Unregister.
                     0x2   PREFER_DISK
                               Use this disk for reading data
                               (= Preferred Disk).
                                  This flag is affected by the command Prefer.
                     0x4   RELEASE_DISK_ON_DISABLEK
                               Sends a SCSI release command to the
                               selected disk on each push button Disable.
                                  Without this flag no SCSI command is issued
                                  on Disable.
example:             .../Parameters/P3C0T0L1       0x6
default:             0x2
remark:              Parameter acts on disk device level




U41115-J-Z145-1-76                                                           31
Registry Entries                                    Background Information



relative path      Parameters/Port<port>
value type         DWORD
bit flags          0x1   EXCLUDE_PORT
                             Don’t use this port for DuplexWrite.
example:           .../Parameters/Port3   0x1
default:           - none -
remark:f           Parameter acts on port level




32                                                         U41115-J-Z145-1-76
Background Information                                          Registry Entries



relative path:       Parameters/StrictChecking
value type:          DWORD
bit flags:           0x1   DW_STRICT_CHECK_COUNT
                               Sets a disk to status Error if its partner disk is
                               missing.
                                  In a 2-node MSCS configuration it might
                                  happen that on accident both nodes see one
                                  disk each, but a different one. This flag is
                                  provided to prevent such a situation which
                                  would lead to inconsistent partner disks.
                                  Keep in mind that setting this bit can lead to a
                                  situation where both disks are set to status
                                  Error!
                     0x2   DW_STRICT_CHECK_SAVE
                               Sets both disks to status Error when both
                               were Online but Save flag not set.
                                  This situation can occur, for example, after an
                                  emergency power down: Data has been
                                  written to the disks, but COD data have not yet
                                  been updated. The disks might be in an incon-
                                  sistent state. It cannot be decided which one
                                  is the most recent.
                                  Without this flag one disk will be selected
                                  randomly and set to status Online. The partner
                                  disk will be set to status Recover.
example:             .../Parameters/StrictChecking    0x3
default:             - none -
remark:              parameter acts globally




U41115-J-Z145-1-76                                                              33
Glossary
Agent
        An agent is the implementation of a network management protocol. An
        agent exchanges information with a manager via, for example, the
        network, devices, systems, or applications.

Alarm
        If an agent detects an unusual operating status in the server, it sends an
        alarm (trap) to the manager.
        An alarm is identified by an alarm level (error class, severity) which is
        displayed in the user interface using an alarm color.

Cluster
      Two or more independent computer systems that are communicated with
      and administered like a single system.

COD
        Abbreviation for Configuration On Disk. Each DuplexWrite Disk has to be
        partitioned into the COD (Configuration On Disk) data area and the user
        partitions. The COD area is a non-standard partition to be used by
        DuplexWrite. It contains DuplexWrite configuration and status data, as
        well as information on the partner disk, last update, and host name.

Device
      A network system (server), router, hub, or any other addressable device
      in the network. It is not a cable, a tap, or a network icon.

Duplex Data Manager
     The Duplex Data Manager combines MultiPath and DuplexWrite and offers
     high availability in terms of connection and storage system failures. In
     combination with MS Cluster Server a full disaster-tolerant configuration
     can be set up.

DuplexWrite
     DuplexWrite is a software to improve the availability of disk storage
     subsystems. DuplexWrite duplicates write operations so that two disks of
     different disk storage subsystems contain identical data.




U41115-J-Z145-1-76                                                             35
Glossary


DuplexWrite Group
     A pair of redundant disks is called a DuplexWrite Group. Both members
     (DuplexWrite Disks) of a DuplexWrite Group contain identical (user) data.
     A DuplexWrite Group appears to the operating system as one disk.
     Duplexing is performed based on disk LUNs, including the virtual LUNs
     of a RAID subsystem. Each DuplexWrite Group has one Preferred Disk -
     by default the first one - where the data is read from.

LUN
       Abbreviation for Logical Unit Number. In the SCSI specification, one level
       lower than the Target-ID. In a RAID environment, mutually independent
       storage areas.

MSCS
       Abbreviation for Microsoft Cluster Server

MultiPath
      MultiPath is a system-oriented software for PRIMERGY servers. It
      supports the use of redundant Fibre Channel connections between the
      server and external storage subsystems and thus increases their avail-
      ability. MultiPath provides protection against the failure of a Fibre
      Channel connection, a hub, or a host bus adapter by maintaining data
      traffic on one of the redundant Fibre Channel connections in the event of
      a failure.

Server
      A server is a device on which a server operating system (Windows NT,
      Novell NetWare, UnixWare) and central software programs are installed.
      Several other devices are connected to a server (clients, workstations,
      desktops) via a network. Depending on the operating system, the server
      can monitor and control the connected devices. In addition, privileges
      can be assigned to the connected devices so that access to the central
      software programs of the server may be more or less restricted.

ServerView
      Software to control important server equipment and functions such as
      hard disks, fans, power supplies or temperature.




36                                                             U41115-J-Z145-1-76
                                                                 Glossary


SNMP
       This abbreviation stands for Simple Network Management Protocol.
       SNMP is a standard management protocol in TCP/IP networks.

Trap
       Warnings that are sent automatically by an agent.




U41115-J-Z145-1-76                                                        37
Figures
Figure 1:    Mass Storage: Device View window       . . . . . . . . . . .    7

Figure 2:    DuplexWrite: Disk List window    . . . . . . . . . . . . . .    9
Figure 3:    DuplexWrite: Disk Group window . . . . . . . . . . . . .       12

Figure 4:    DuplexWrite: Disk Info window    . . . . . . . . . . . . . .   17

Figure 5:    DuplexWrite: Config Disk group window      . . . . . . . . .   19
Figure 6:    COD partition . . . . . . . . . . . . . . . . . . . . . . .    23




U41115-J-Z145-1-76                                                          39
Tables
Table 1:   Notational conventions . . . . . . . . . . . . . . . . . . . .    2

Table 2:   DuplexWrite status icons . . . . . . . . . . . . . . . . . . .   21




U41115-J-Z145-1-76                                                          41
Related publications
Please contact your local office for ordering the manuals.

 [1]   ServerView - Server Management
       User Guide
       Target group
       System administrators, technicians

 [2]   MultiPath
       Product Manual
       Target group
       System administrators, technicians




U41115-J-Z145-1-76                                           43
Index
A                            S
Action on Selected Disk 14   SCSI 28
                             SCSI bus 10
C                            ServerView 1, 5, 7, 15
cluster 5                    standalone version 1, 9
COD 23, 30                   storage subsystem 1, 29
D                            T
Data Duplexing 29            Textbox Message 15
Data Recovery 30
data structures 1, 29
deinstallation 6
Disk Errors 24
Disk Group 12, 17
Disk List 11
Duplex Data Manager 5
Duplex Disk 8
DuplexWrite Disk 23
DuplexWrite Group 30
DuplexWrite group 8
DW Configure 8
DWrite Status 8, 10

F
Fibre Channel 1, 29

G
Global Buttons 16

I
installation 5

M
MS Cluster Server 26
MSCS 5, 26
MultiPath 29

R
RAID 29
Registry Entries 31




U41115-J-Z145-1-76                                     45
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                                              Corrections
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    Fax: (++49) 89636-52003                                                    Self-tuition media

    The Siemens Training Center offers consulting for in-service training, courses and self-tuition media on almost all
    aspects of information technology, either on your premises or at a Training Center near you. Write to us for infor-
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