Article ID: 888562
Article Last Modified on 10/30/2006
APPLIES TO
- Microsoft Windows Server 2003, Enterprise Edition (32-bit x86)
- Microsoft Windows Server 2003, Standard Edition (32-bit x86)
- Microsoft Windows 2000 Advanced Server
- Microsoft Windows 2000 Server
Important This article contains information about modifying the registry. Before you modify the registry, make sure to back it up and make sure that you understand how to restore the registry if a problem occurs. For information about how to back up, restore, and edit the registry, click the following article number to view the article in the Microsoft Knowledge Base:
256986 Description of the Microsoft Windows Registry
SYMPTOMS
You are running the Server Message Block (SMB) protocol with Terminal Server enabled on a Microsoft Windows Server 2003-based server or on a Microsoft Windows 2000 Server-based server. In this scenario, when you try to access files on a client computer that is running Windows 2000 Server or Microsoft Windows NT 4.0, you may experience slow performance. It may take 30 to 60 seconds to complete a task. Typically, the delay will last exactly 35 seconds.
CAUSE
This problem occurs if several Remote Desktop Protocol (RDP) client computers connect to the server at the same time. The number of outstanding SMB requests that are sent from the RDP client computers to the server may exceed the default maximum of 50 connections. When this behavior occurs, other SMB requests must wait in the redirector on the client computer until the earlier requests are answered or canceled, or until a time-out error occurs.
The MaxMpxCt parameter is set in the registry to specify the maximum number of simultaneous client computer requests that can be made to a particular server. When the client computer first establishes a connection with the server, the MaxMpxCt parameter value is passed from the server to the redirector on the client computer. The limit on outstanding requests is enforced by the redirector on the client computer.
Typically, each RDP client computer is running the Explorer.exe process. When several RDP client computers are connected to the server, Microsoft Internet Explorer makes extensive use of directory notifications. This behavior causes several NTNotifyDirectoryChange SMBs to be posted to the server. These NTNotifyDirectoryChange SMBs enable the server to notify the client computer when file or directory information changes.
The NTNotifyDirectoryChange SMB is classified as a long term request. The server receives the NTNotifyDirectoryChange SMB. However, the server does not return the NTNotifyDirectoryChange SMB until a change occurs or until the NTNotifyDirectoryChange SMB is canceled by the client computer.
When several RDP client computers connect to the server, the number of outstanding commands against the server may exceed the default maximum of 50. When this behavior occurs, other SMB requests must wait in the redirector until the earlier requests are answered, or canceled, or until a time-out error occurs.
RESOLUTION
Warning If you use Registry Editor incorrectly, you may cause serious problems that may require you to reinstall your operating system. Microsoft cannot guarantee that you can solve problems that result from using Registry Editor incorrectly. Use Registry Editor at your own risk.
To resolve this problem, you must change the value of the MaxCmds parameter and the MaxMpxCt parameter in the registry of the server and of the client computer. The maximum number of connections that can be made is determined by the lesser of the MaxCmds parameter or the MaxMpxCt parameter. The explicit number is sent from the server to the client computer during the negotiation phase when you set up an SMB session.
To change the value of the MaxCmds parameter and the MaxMpxCt parameter on the server and on the client, follow these steps:
- On the client computer, click Start, click Run, type regedit, and then click OK.
- Locate and then click the following subkey:
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\LanmanWorkstation\Parameters
- Right-click Parameters, point to New, and then click DWORD Value.
- Type MaxCmds, and then press ENTER to name the new entry.
- Right-click MaxCmds, and then click Modify.
- In the Base area, click Decimal.
- In the Value data box, type 1024, and then click OK.
- Quit Registry Editor.
- On the server, click Start, click Run, type regedit, and then click OK.
- Locate and then click the following subkey:
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\lanmanServer\parameters
- Right-click Parameters, point to New, and then click DWORD Value.
- Type MaxMpxCt, and then press ENTER to name the new entry.
- Right-click MaxMpxCt, and then click Modify.
- In the Base area, click Decimal.
- In the Value data box, type 1024, and then click OK.
- Quit Registry Editor.
MORE INFORMATION
The most common symptom of this problem is when the server sends an oplock break request regarding a locked file to the client computer. If the client computer has received the maximum number of outstanding requests, it cannot send the oplock break response to the server. When this behavior occurs, input/output (I/O) between the client computer and the server stalls until the OplockBreakWait timer expires on the server. The default value of the OplockBreakWait timer is 35 seconds.
To verify that the symptoms that you experience are caused by the problem that is discussed in this article, you must view a Network Monitor trace. For additional information about how to view a Network Monitor trace, click the following article number to view the article in the Microsoft Knowledge Base:
812953 How to use Network Monitor to capture network traffic
The Network Monitor trace will appear similar to the following:
395 0.005213 TSECLIENT FileServer SMB C transact2 Query path info, File = \dir1\subdir1\filename.xls IP
396 0.000083 FileServer TSECLIENT SMB R transact2 Query path info (response to frame 395) IP
397 0.001951 TSECLIENT FileServer SMB C transact2 Query file system info IP
398 0.000027 FileServer TSECLIENT SMB R transact2 Query file system info (response to frame 397) IP
399 0.002763 TSECLIENT FileServer SMB C transact2 Query path info, File = \dir1\subdir1\filename.xls IP
400 0.000073 FileServer TSECLIENT SMB R transact2 Query path info (response to frame 399) IP
401 0.000869 TSECLIENT FileServer SMB C transact2 Query path info, File = \dir1\subdir1\filename.xls IP
402 0.000065 FileServer TSECLIENT SMB R transact2 Query path info (response to frame 401) IP
The query from the client computer will appear similar to the following:
403 0.000603 TSECLIENT FileServer SMB C NT create & X, File = \dir1\subdir1\filename.xls IP
There will be a lock on the file. The server will ask the client computer to break the lock on the file. This request will appear similar to the following:
404 0.018093 FileServer TSECLIENT SMB C lock & X, FID = 0xae37, Unlocks = 0 (0x62 for 0x3c0000) IP
The client computer will acknowledge the request from the server on the TCP level, but not on the SMB level. If this behavior occurs, the client computer will not respond to the server, and the Network Monitor trace will appear similar to the following:
405 0.100696 TSECLIENT FileServer TCP Control Bits: .A...., len: 0, seq: 765791988-765791988, ack:2687722727, win:63772, src: 1314 dst: 139 (NBT Session) IP
If the client computer does not respond to the server within a specified time, the server will send an oplock break request to the client computer. If the client computer does not respond to the oplock break request from the server within a specified time, the OplockBreakWait timer that is on the server will expire. When this behavior occurs, the Network Monitor trace will appear similar to the following:
406 34.901136 FileServer TSECLIENT SMB R NT create & X, FID = 0xae3e IP
407 0.000309 TSECLIENT FileServer SMB C transact2 Query path info, File = \dir2\subdir2 IP
For additional information, click the following article numbers to view the articles in the Microsoft Knowledge Base:
191370 Slow network performance with Terminal Server
271148 MaxMpxCt and MaxCmds limits in Windows 2000
296264 Configuring opportunistic locking in Windows
The third-party products that this article discusses are manufactured by companies that are independent of Microsoft. Microsoft makes no warranty, implied or otherwise, regarding the performance or reliability of these products.
Additional query words: TS
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