DOCUMENT:Q154941  07-MAR-2002  [exchange]
TITLE   :XADM: How to Determine Which Public Folder Replica is Used
PRODUCT :Microsoft Exchange
PROD/VER::5.5
OPER/SYS:
KEYWORDS:kbusage exc55

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The information in this article applies to:

 - Microsoft Exchange Server, version 5.5 
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SUMMARY
=======

In Microsoft Exchange Server, replicas of public folders can be present on
several Exchange Server computers in different Exchange Server sites of the
Exchange Server organization.

This article describes the algorithm that is used to determine which public
folder replica is accessed when a user tries to open the contents of a public
folder.

MORE INFORMATION
================

The algorithm is as follows:

 - If an instance of the public folder exists on the user's Public Folder
   Server, that instance is used. The Public Folder Server is determined by the
   Public Folder field on the General property page for the client's private
   information store.

 - If there is an instance of the public folder on any server with the same
   "Server Location" as the Public Folder Server.

 - Next, any server in the server location * is checked.

 - If the client has an existing remote procedure call (RPC) connection to a
   server, it is tried next.

 - If there are several instances in the site, the information store uses a
   per-computer random number (called a connection modulus) to determine which
   server in the site it will connect to. This specifies a per-computer method
   of determining the connection. In other words, two different users on the
   same computer will connect to the same server to view the public folder.

   Because the connection modulus is random per computer, this method will
   distribute connections across all the available instances in the site. This
   provides load balancing to servers within the site.

   NOTE: The connection-modulus server may not be the same for a client for all
   public folders. For example, if SERVER1 is the user's Public Folder Server,
   and SERVER2 and SERVER3 are other Public Folder Servers in the same site that
   contain replicas of a public folder, FOLDER1. The user's connection-modulus
   server could be SERVER3. Now, suppose there is another public folder,
   FOLDER2, for which SERVER2, SERVER3, and SERVER4 are Public Folder Servers
   containing replicas of this folder. In this case, the user's
   connection-modulus for FOLDER2 might be SERVER2.

 - If the connection modulus server cannot be connected to, the remaining
   servers in the site with the replicas are tried.

 - If no instances are available in the site, but there is at least one site
   available with instances, the affinity to the sites is used to rank the order
   in which connections to the sites will be attempted. The affinity is set on
   the site public folder Affinity page. It allows an administrator to set a
   cost to each of the other sites in the enterprise.

   The cost ranks the order in which the client will attempt connection, and the
   lowest cost site is attempted first. After the site is determined, its
   servers are tried in random order. If two sites have the same cost, the
   servers in those sites are pooled together and tried in a random order.
   Connections to servers in sites without an affinity setting are not
   attempted.

   NOTE: Clients must have RPC connectivity to the servers in the affinity sites.
   Otherwise, the clients will not be able to access the public folders in the
   other sites, even though the affinity has been correctly set.

The cost ranks the order the client will attempt connection and the lowest cost
site is attempted first. After the site is determined, its servers are tried in
random order. If two sites have the same cost, the servers in those sites are
pooled together and tried in a random order. Connections to servers in sites
without an affinity setting are not attempted.

NOTE: Clients must have RPC connectivity to the servers in the affinity sites.
Otherwise, the clients will not be able to access the public folders in the
other sites, even though the affinity has been correctly set.


Additional query words: hang

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Keywords          : kbusage exc55 
Technology        : kbExchangeSearch kbExchange550 kbZNotKeyword2
Version           : :5.5
Issue type        : kbinfo

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