SNA Server PU/LU Reactivation Fails After VTAM Z NET CANCEL

• Microsoft SNA Server versions 3.0, 3.0 SP1, 3.0 SP2

SYMPTOMS

When Microsoft SNA Server is configured with one or more channel connections over the Polaris Escon channel adapter, not all of the PUs and LUs reactivate if VTAM is shut down quickly using the VTAM command:

   z net, cancel

This problem was observed when SNA Server was configured with 15 PUs and 250 LUs each (3750 total LUs). Some LUs failed to reactivate when VTAM was restarted.

CAUSE

There are two different problems contributing to the reactivation problems:

• SNA Server is not efficiently processing a large number of DACTLU messages from the host, causing slow performance in responding to DACTLU requests. This may cause the host to experience channel timeout errors during LU deactivation. This problem was fixed in SNA Server 3.0 Service Pack 2 (SP2), though was not listed in the 3.0 SP2 fix list Help file.
• The Polaris link service is not responding quickly to SNA Server Close(Link) requests, causing the host to experience channel errors when attempting to reactivate the PUs and LUs when the host was brought back up again.

WORKAROUND

To work around this problem, do one of the following:

• Stop VTAM using an orderly shutdown method, instead of using the "z net, cancel" option.

  -OR-

• Try disabling the channel PUs first

        v net, id=xxxx,inact,f
  

  before issuing the "z net, cancel ..." command.

STATUS

Microsoft has confirmed this to be a problem in the SNA Server version 3.0, 3.0 Service Pack 1 (SP1) and 3.0 SP2. A supported fix is now available, but has not been fully regression tested and should be applied only to systems experiencing this specific problem. Unless you are severely impacted by this specific problem, Microsoft recommends that you wait for the next Service Pack that contains this fix. Contact Microsoft Technical Support for more information.

MORE INFORMATION

With this fix applied, SNA Server 3.0 was successfully tested with 15,000 LUs (the maximum LU capacity supported by SNA Server 3.0) over a single Polaris ESCON adapter (60 PUs, each with 250 LUs).

The fix described in the following Microsoft Knowledge Base article should also be applied when using SNA Server with thousands of 3270 or LUA LUs:

   Article ID: Q176020
   Titile    : SNA Server Starts Slowly When Configured with 15000 3270
               LUs