The information in this article applies to:
- Microsoft Exchange Server version 4.0
SUMMARY
In Microsoft Exchange Server, replicas of public folders could be present
on several Microsoft Exchange Servers in different Microsoft Exchange
Sites of the Microsoft Exchange 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
- 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 (IS).
- If there is no instance on the user's server, but there is one instance
in the Site, that instance is used.
- If there are several instances in the Site, the IS 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.
Since 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 could be SERVER2.
- If the connection modulus server cannot be connected to, the remaining
Servers in the Site with the replicas are tried. Those Servers that
already have an RPC connection with the client are tried first.
- 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 the client will attempt connection and the lowest
cost Site is attempted first. Once 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.
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