SQL Server 2008 R2 Drops Connections when Anti-Virus Scan is running I have a SQL Server 2008 R2 Enterprise (SP2) cluster (2 nodes Windows Server 2008 R2 SP1, NetApp Shared storage).

There are 5 instances all running on this cluster in an active passive configuration and we have found that occasionally during the time that the weekly antivirus scan runs, one of the instances starts to drop connections and becomes inaccessible for about an hour (the scan runs for 2 hours), all the other instances are fine.

In the error log, we see the following messages when the server is inaccessible:


  TCP connection closed but a child process of SQL Server may be holding
  a duplicate of the connection's socket.  Consider enabling the
  TcpAbortiveClose SQL Server registry setting and restarting SQL
  Server. If the problem persists contact Technical Support.
  
  Error: 26073 Severity: 16 State: 1.


They are also accompanied by the following error (although not all the time):


  Process 0:0:0 (0x15540) Worker 0x0000000E721041A0 appears to be
  non-yielding on Scheduler 20. Thread creation time: 13025544955370.
  Approx Thread CPU Used: kernel 0 ms user 0 ms. Process Utilization
  0%. System Idle 91%. Interval: 119402 ms.


During this time there are also some warnings with IO operations taking longer than 15 seconds to complete.

What I'd like to know is:

We have excluded all the locations recommended by Microsoft from scanning, so why is this only happening during the scan, can these issues just be caused by the extra load of the scan, they're pretty powerful boxes so I wouldn't have thought that the extra load would cause a problem, and the time at which this runs, the server is not busy, also if it is caused by the scan why does the problem only stay for 1 hour rather than the full 2?

What is the TcpAbortiveClose registry setting and what are the implications of this setting, I know how to set it from the Microsoft KB article(http://support.microsoft.com/kb/2491214), but I can't find any documentation on this setting anywhere on what it does or whether it is a good idea.
I see that you are still running SQL Server 2008 R2 SP1, so I would suggest that you update your software.  If you update to SQL Server 2008 R2 SP2 CU 2 there is a fix for this problem.  

You can read about this particular problem at: http://support.microsoft.com/kb/2491214

I would recommend not applying the "workaround" but just getting up-to-date with SP2 CU2 (at least).  You should know that SP2 CU8 is available.