CHAPTER 18

                     PUBLIC FOLDER REPLICATION

 

 

 

Lesson 1:  Public Folder Strategies

 

Both single and multiple public folder instances have advantages and disadvantages that you need

to take into consideration when planning your public folder strategy.

 

 

Stand-Alone Public Folders

 

Stand-alone public folders are the default configuration, but they may or may not be ideal for

your purposes. 

 

 

  •   Advantages.  Immediate replication.
  •   Disadvantages.  Slow access, and no fault tolerance.  Good idea to make a replica, for when

you are performing system maintenance.

 

 

Advantages of Public Folder Replicas

 

  •   A replica of a public folder can be kept available in all locations for local access.
  •   Client access over WAN connections can be eliminated.
  •   Fault Tolerance between multiple servers is available.
  •   Load balancing between multiple servers is possible.
  •   Public folder replication can be scheduled.
  •   New items posted in a public folder instance are not immediately available in all other

locations due to public folder replication latency.

 

 

Public Folder Instance Between Organizations

 

The InterOrg Replication utility should be used, which is available on the Exchange 2000

Server CD in the \Support\Exchsync\I386 directory.

 

A replication configuration tool (EXSCFG.EXE), which is part of the InterOrg Replication

utility, facilitates the configuration task.

 

NOTE:  Make sure that the SMTP address of the original mailbox-enabled user account

matches the underlying e-mail address of the mail-enabled contact object.

 

 

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Disadvantages of Dedicated Mailbox Servers

 

You would have to delete the public store associated with the default Messaging Application

Programming Interface (MAPI-based) hierarchy from the mailbox servers.  A default public

store on another server must then be specified for all local mailbox to provide access to the

MAPI-based public folder hierarchy.

 

Use Exchange System Manager to place all top-level folders on a dedicated public folder

server and configure their replication if desired.

 

 

Lesson 2:  Public Folder Replication Configuration

 

 

Public folder replication usually refers to the process of replicating public folder contents.

 

 

Public Folder Replication Overview

 

Public folder replication guarantees that changes made to one instance overwrite earlier

information in other instances to ensure the uniformity of data.

 

 

Network Topology Independence

 

Even within a single routing group, the Information Store service of the local server does

not contact any Information Store running on other servers directly.

 

Replication can take a long time if there are a lot of nested folders.

 

 

Public Folder Replication Agent (PFRA)

 

PFRA is an internal component of the Information Store service, and is responsible

for replicating the public folder content.

 

  • Default, replication every 5 minutes.
  • Maximum size of 2GB for each e-mail sent.

 

 

 

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Collecting Public Folder Instances

 

To add a public folder replica from another server to the public store on your server, right-click Public

Folder Instances, point to All Tasks, and click Add Replica.

 

The default message size limit is 300KB

 

NOTE:  It is possible to define maximum message size limits per SMTP virtual server and routing

group connectors.  However, public folder replication messages are system messages, which are

unaffected by these size limits.  Because large replication messages can disrupt interpersonal

message transfer, it is advisable to set appropriate maximum item sizes per replicated public

folder or optimize the replication schedule.

 

 

Configuring Age Limits per Replica

 

To achieve this configuration, in the folder’s Limits tab, clear the Use Public Store Defaults check

box and, under Age Limit For Replicas (Days), type 60.  Now you need to configure one

exception for the replica for the server where you want to apply a limit of 10 days.

 

 

Replication of System Folders

 

Using Exchange System Manager, you can view the list of all system folders that exist when you

right-click the desired hierarchy object under the Folders container and select View System Folders.

 

  • Events Root.
  • EFORMS REGISTRY
  • OFFLINE ADDRESS BOOK
  • SCHEDULE+FREE/BUSY.
  • Schema
  • Store Events

 

 

Moving a Public folder Between Servers

 

You only need to add a public folder replica to a new server and remove the old instance from the

first machine.  In the public folder’s Replication tab, use the Add and Remove buttons for this

purpose.

 

 

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Replication, for example, is not an exceptionally fast process, and, if you remove the original

replica too quickly, users might end up with an empty folder in Outlook 2000.

 

 

Exercise Summary:

 

  •   Using Exchange System Manager, you can configure public folder replicas in various ways.  You

can add replicas through the Public Folder Instances object or by means of each individual folder’s

  •   Replication tab.
  •   Public folder replication may require some time, but as soon as replicas are synchronized, all users

have seamless access to the resources.

 

 

Lesson 3:  Public Folder Replication Process

 

Public folder replication is a very complex process.  When you add replicas to a public store, the

PFRA must fill the new instances.  As change occur on any replica, those changes must be

replicated and possible replication conflicts must be detected.

 

 

Public Folder Replication Transport Mechanism

 

If there is a problem sending an e-mail you will get a garbled message in the form of WINMAIL.DAT.

 

NOTE:  By addressing more than one remote Information Store within a single replication message,

the use of WAN connections and any other e-mail paths is optimized.  Similar to an interpersonal

message sent to multiple users, the Exchange 2000 Server transfers only on message. Messages are

split into multiple instances at the very last point when separate paths must be used.

 

 

Monitoring Message State Information

 

Message state information describes the collection of change numbers, time stamps, and

predecessor change lists, which the PFRA uses to determine most recent items as they are

replicated between public folder instances.

 

The following are the elements of message state information:

 

  • Change number. 
  • Predecessor change list
  • Time stamp

 

 

 

 

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Change Number

 

Change numbers identify public folder and content modifications.  They are created using the GUID

of the information store and a server-specific change counter.

 

 

Predecessor Change List

 

The predecessor change list permits the PFRA to detect folder replication conflicts.  It maintains a

list of all Information Store services that have every made changes to an object and their server-

specific change counters.

 

 

Time Stamp

 

Time Stamp never decreases but always increases.

 

 

Message Deletion

 

Every PFRA that receives the notification message identifies and deletes the objects from its public

folder replica.

 

 

Replicating Item Modifications

 

All PFRAs exchange modifications directly with each other.  It is possible that a particular replica

 receives old replication information, and in this case existing items should not be replaced.

 

 

Out-of-Sync Public folders and Backfill

 

The local public folder status switches to In Sync right away.  Therefore, there is a fair chance that

the folders are not synchronized although their status indicates differently.

 

Backfill

 

If the remote replica contains more modifications than the local instance, a backfill request is returned

to the remote PFRA, which includes the old replica-specific change number of the remote PFRA.

 

 

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The following situations automatically initiate a backfill request:

 

  • A public server has been restored from a backup.
  • A public server was down while changes occurred.
  • A replication message has been lost.

 

 

Adding Replicas

 

The PFRA assigns the current change number, time stamp, and a fresh predecessor change list to

each new object.  It also does this for new public folder replicas.  The change number of the new

replica, however, does not yet exist on the predecessor change list of any other instance.

 

 

Deleting Replicas

 

The deletion of a replica eliminates its reference within the properties of the public folder object.

 

 

Public Folder Conflict Resolution

 

The PFRA replaces older objects with more recent items, but which item does the PFRA replace

in the event of a replication conflict, where two objects are both considered the most recent? 

Users can save 1 or both messages.

 

Chapter Summary:

 

  •   Instead of having all users access single instance somewhere, you can provide a public folder

replica locally for faster and more reliable client access.  Public folder replication works within

an organization.  Between organizations, replication is supported by means of the InterOrg

  •   Replication utility.
  •   By checking the state information, the most recent items can be detected.
  •   Replication conflicts must be resolved manually.  The PFRA will send public folder

conflict messages, including the conflicting items as attachments, to the users who created the

      conflict and the public folder owners.