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Q185446: TN3270 Server LUA Pool Use Should Load Balance Across Servers

Article: Q185446
Product(s): Microsoft SNA Server
Version(s): WINDOWS:4.0
Operating System(s): 
Keyword(s): 
Last Modified: 22-SEP-1999

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The information in this article applies to:

- Microsoft SNA Server, version 4.0 
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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:

  Q128244 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:

  Q182139 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.

Additional query words:

======================================================================
Keywords          :  
Technology        : kbAudDeveloper kbSNAServSearch kbSNAServ400
Version           : WINDOWS:4.0
Issue type        : kbprb
Solution Type     : kbnofix

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