Windows 2003 SP2 TCP Offload Engine Incompatibility

XenData Technical Note XTN905

July 29, 2009

Copyright 2009 XenData Limited. All rights reserved.

Introduction

The TCP Offload Engine is relatively new functionality that is supported in Windows 2003 SP2 and with some network interface hardware. It is intended to reduce the load on the computer's CPU by offloading TCP/IP handling to processing hardware in the NIC. The TCP Offload Engine is enabled by default in Windows 2003 SP2 for network interface cards that support this functionality.

When enabled in Windows 2003 SP2, the TCP Offload Engine can cause a wide range of problems including:

  • TCP data streams become corrupted
  • Non-paged pool (KERNEL) memory becomes exhausted
  • Browsing the Public and/or Default Website in IIS results in error "Page cannot be displayed".

Example NIC with TCP Offload Engine

The popular HP DL380 G5 server is commonly used for XenData Archive Series software installations. This server uses the HP NC373i built-in NICs which provide TCP Offload Engine functionality and is an example network interface that is prone to the problems described in this technical note .

MX64 Specific Problem

In the case of the XenData MX64 Edition, when network interfaces that support the TCP Offload Engine (such as the HP NC373i) are used for the private network that connects datamovers to the master server, problems may occur with restores of large files. The symptoms are:

  • The file transfer rate from tape to disk and RAM on the datamover is not affected and is typically better than 100 MB/s. This is identified in the XenData Management Console System display.
  • The file transfer rate from the datamover may start high but drops to a very low level as a large file is restored.

Problem Correction

Microsoft has released a  hotfix rollup package (http://support.microsoft.com/kb950224)  to fix this issue. This is suitable for new XenData installations and should be implemented before the XenData software is installed. However if this patch is installed after the XenData system is configured, the patch may write files to the XenData share.  To fix the problem for an existing XenData installation, rather than implement the hotfix, a registry change should be made: 

Using regedit, go to the following key:

 HKey_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters 

Change the value of EnableTCPChimney from 1 to 0. 

More Information

The following links to Microsoft Knowledge Base articles provide more information:

http://support.microsoft.com/kb/945977 - Some problems occur after installing Windows Server 2003 SP2

http://support.microsoft.com/kb/948496 - An update to turn off default SNP features is available for Windows Server 2003-based and Small Business Server 2003-based computers

http://support.microsoft.com/kb/950224 - A Scalable Networking Pack (SNP) hotfix rollup package is available for Windows Server 2003

Applicability

XenData installations that run Windows 2003 SP2 (X64 and 32 bit) which employ a NIC with TCP Offload Engine functionality.