Microsoft KB Archive/185446

= TN3270 Server LUA Pool Use Should Load Balance Across Servers =

Article ID: 185446

Article Last Modified on 10/22/2003

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APPLIES TO


 * Microsoft SNA Server 4.0

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This article was previously published under Q185446



IMPORTANT: This article contains information about editing the registry. Before you edit the registry, make sure you understand how to restore it if a problem occurs. For information about how to do this, view the "Restoring the Registry" Help topic in Regedit.exe or the "Restoring a Registry Key" Help topic in Regedt32.exe.



SYMPTOMS
If an LUA Pool is defined with LUA LUs owned by more than one SNA Server, and that LUA Pool is assigned to an SNA Server TN3270 Service, the TN3270 Service will exhaust all sessions owned by the local SNA Server before attempting to open LUs owned by other SNA Servers.



CAUSE
This behavior is by design.



STATUS
Microsoft has confirmed this to be a problem in SNA Server version 4.0. However, an update to SNA Server 4.0 is available to allow load balancing of TN3270 sessions across available SNA Server computers. This problem has been corrected in the latest U.S. Service Pack for SNA Server version 4.0. For information on obtaining the Service Pack, query on the following word in the Microsoft Knowledge Base (without the spaces):

S E R V P A C K



MORE INFORMATION
Although this behavior is by design, there have been requests to support an option for TN3270 that allocates LUA sessions across SNA Servers which own LUs from the pool, so that load balancing of session use across multiple SNA Server computers can occur.

Note that this feature does not provide TN3270 client load balancing across more than one TN3270 server. That function must be provided by the TN3270 client or possibly the TCP/IP name service being used. If this functionality is needed, SNA Server provides transparent client load balancing across SNA Server computers using its native 3270 interface. For additional information about SNA Server load balancing, please see the following article in the Microsoft Knowledge Base:

128244 SNA Server Load Balancing and Hot Backup

For additional information about shared LUA pool use by more than one TN3270 server, please see the following article in the Microsoft Knowledge Base:

182139 LUA Pool Cannot Be Assigned to Two TN3270 Servers

WARNING: Using Registry Editor incorrectly can cause serious problems that may require you to reinstall your operating system. Microsoft cannot guarantee that problems resulting from the incorrect use of Registry Editor can be solved. Use Registry Editor at your own risk.

For information about how to edit the registry, view the "Changing Keys And Values" Help topic in Registry Editor (Regedit.exe) or the "Add and Delete Information in the Registry" and "Edit Registry Data" Help topics in Regedt32.exe. Note that you should back up the registry before you edit it.

After this update is applied to the SNA Server where the TN3270 Service is running, the following registry entry must be set to enable TN3270 load balancing behavior:   KEY_LOCAL_MACHINE\System\CurrentControlSet\Services \TN3270\Parameters ReslocFlags: REG_DWORD: 1

1 = "load balance" across SNA Server computers 0 = default if not defined (old behavior - try local server first) If the ResLocFlags registry entry is set to 0x01, TN3270 will alternate between SNA Server computers when attempting to open an LUA pool. This will cause the session load to be shared among SNA Server computers who own LUs from this LUA pool.

After this update is applied and the ResLocFlags entry is set, the SnaBase service and TN3270 service must be restarted for the change to take effect.

Keywords: kbnofix kbprb KB185446

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