Topic Last Modified: 2006-07-13

The Microsoft® Exchange Server Analyzer Tool examines the Exchange Function Call Log (FCL), the Store.fcl file, to determine the number of current, ongoing cross-component calls from the Microsoft Exchange Information Store service (Store.exe) to the Virus API (VAPI) component.

The Exchange Server Analyzer also queries the ScanningThreads key from the following registry entry to determine the maximum number of threads allowed for VAPI component calls:

HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\MSExchangeIS\VirusScan

Ongoing calls are requests from the Microsoft Exchange Information Store service (Store.exe) to other components that have not received a response at the time the Exchange FCL data is written to the Store.fcl file.

If the Exchange Server Analyzer finds that the number of ongoing calls from the Exchange Information Store service (Store.exe) to the VAPI component approaches the maximum number of threads allowed, the Exchange Server Analyzer displays an error.

When cross-component calls from the Microsoft Exchange Information Store service (Store.exe) wait for a response, remote procedure call (RPC) threads can back up behind these requests and lead to Exchange Server performance issues such as delays in server responses to clients.

Ongoing calls from the Microsoft Exchange Information Store service to the VAPI component can be caused by conditions:

• Updates to a virus scanner which generate a re-scan of items in the information store.
  
  
• A misconfigured virus scanner
  
  
• Virus scanner software processes a large message or attachment
  
  

To resolve this error, take the following steps:

• Schedule updates to your virus engine for times when resource consumption is low, that is, off-peak demand intervals.
  
  
• Consider reinstalling the virus scanning software, but reinstall at off-peak demand intervals.
  
  
• Examine the configuration of your virus scanning engine for the correct thread configuration, file level exclusions, and so on. See Microsoft Knowledge Base article 823166, "Overview of Exchange Server 2003 and antivirus software" (http://go.microsoft.com/fwlink/?linkid=3052&kbid=823166).
  
  
• Increase the thread count for the virus scanning API:
  
  The optimal value for ScanningThreads is equal to (2 * NumberOfProcessors) + 1. For example, on a server running Exchange Server That has two processors, the optimal value for ScanningThreads is 5.
  
  

  Note:
  If hyper-threading is enabled, the value for NumberOfProcessors will be double the number of physical processors. It is recommended that you check with your antivirus software manufacturer to determine whether physical or logical processors should be used in this formula.

To increase the thread count

1. Open a registry editor, such as Regedit.exe or Regedt32.exe.

2. Navigate to: HKLM\System\CurrentControlSet\Services\MSExchangeIS\VirusScan

3. In the right pane, double-click ScanningThreads.

4. Enter the value returned from the previous formula.

5. Close Registry Editor, and then restart the Microsoft Exchange Information Store service for the change to take effect.

Before you edit the registry, and for information about how to edit the registry, see the Microsoft Knowledge Base article 256986, "Description of the Microsoft Windows Registry" (http://go.microsoft.com/fwlink/?linkid=3052&kbid=256986).

• Review the articles in the For More Information section of this document.
  
  

For More Information

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