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Replication and Backfill Processes

 

Topic Last Modified: 2005-05-06

Replication is largely the same in a mixed-mode topology as it is in a pure Exchange Server 2003 topology. The primary exceptions are the following:

  • Directory objects   As described in Connection Agreements and Public Folder Replication, Active Directory Connector (ADC) ensures that the appropriate public folder directory objects exist in both Active Directory and the Exchange directory. However, the replication processes that ADC uses to synchronize these objects between Exchange Server 2003 and Exchange Server 5.5 do not replace the normal public folder replication processes. The following figure shows the different functions of the different types of processes.
  • Attributes that have changed format   The primary issue is access control. Exchange Server 2003 access control information uses a format different from that used by Exchange Server 5.5. Because Exchange Server 5.5 cannot use the Exchange Server 2003 format, Exchange Server 2003 handles the process of converting from one format to the other. For more information about this conversion and its implications, see Public Folder Access Control in Mixed Mode.
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To illustrate how replication works in a mixed-mode topology, consider the following examples. The first example discusses replication from Exchange Server 2003 to Exchange Server 5.5, and the second example discusses replication from Exchange Server 5.5 to Exchange Server 2003.

Consider a simple mixed-mode topology that has public folders on one computer running Exchange Server 5.5 and one computer running Exchange Server 2003. This is the same topology as that shown in the figure above. An administrator connected to the computer running Exchange Server 2003 adds a new public folder to the tree, and configures it to have content replicas on both servers. The process Exchange uses to complete the new configuration includes the following:

  1. Using the public folder information in Active Directory, ADC creates a new object for the public folder in the Exchange directory.
  2. The computer running Exchange Server 2003 (ExchServ02) sends a hierarchy message to the computer running Exchange Server 5.5 (ExchServ01). The hierarchy message contains the update to the public folder tree structure, and the attributes of the new folder (converted to Exchange Server 5.5 format if needed).
  3. Content replication and backfill then proceed normally as follows:
    1. ExchServ02 adds ExchServ01 to the local copy of the folder's replica list.
    2. ExchServ01 sends a status request to ExchServ02.
    3. ExchServ02 sends a status message to ExchServ01 that includes the full CNSet of the folder.
    4. ExchServ01 determines that all the folder content is missing and records the appropriate entries in the backfill array.
    5. If the content is still missing when the backfill time-out elapses, ExchServ01 creates a backfill request and sends it to ExchServ02.
    6. ExchServ02 compiles the content messages and sends them to ExchServ01.
    7. ExchServ01 uses the incoming content messages to update the folder content and related tracking information.
    8. If change numbers still appear to be missing, ExchServ01 waits 24 hours, and then sends an updated backfill request.
    noteNote:
    Exchange Server 5.5 does not have the backfill improvements that Exchange Server 2003 has. For more information, see Controlling Exchange Server 2003 Public Folder Replication.

In this example, using the same mixed-mode topology that is used in scenario 1, a user with appropriate permissions connected to the computer running Exchange Server 5.5 adds a new public folder to the tree. An administrator configures the folder to have content replicas on both servers. The process Exchange uses to complete the new configuration includes the following:

  1. Using the public folder information in the Exchange directory, ADC creates a new object for the public folder in Active Directory.
  2. The computer running Exchange Server 5.5 (ExchServ01) sends a hierarchy message to the computer running Exchange Server 2003 (ExchServ02). The hierarchy message contains the update to the public folder tree structure and the attributes of the new folder.
  3. ExchServ02 converts attributes such as the access control information to the Exchange Server 2003 format.
  4. Content replication and backfill then proceeds as follows. This process is the same as for a native-mode Exchange topology:
    1. ExchServ01 adds ExchServ02 to the local copy of the folder's replica list.
    2. ExchServ02 sends a status request to ExchServ01.
    3. ExchServ01 sends a status message to ExchServ02 that includes the full CNSet of the folder.
    4. ExchServ02 determines that all the folder content is missing and records the appropriate entries in the backfill array.
    5. If the content is still missing when the backfill time-out elapses, ExchServ02 creates a backfill request and sends it to ExchServ01.
    noteNote:
    If the system included more than one computer running Exchange Server2003 that supports public folders, ExchServ02 looks for another computer running Exchange Server2003 to use as a backfill server before sending the request to the computer running Exchange Server5.5.
    1. ExchServ01 compiles the content messages and sends them to ExchServ02.
    2. ExchServ02 uses the incoming content messages to update the folder content and related tracking information.
    3. If change numbers still appear to be missing, ExchServ02 waits 24 hours, and then sends an updated backfill request.
 
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