How to modify the default SizReqBuf value in Windows 2000 and Windows Server 2003


This article describes how to modify the size of the SizReqBuf value. In File and Printer Sharing for Microsoft Networks, the SizReqBuf value determines how much data is buffered at one time to send to a client. The default values in Microsoft Windows 2000 and in Microsoft Windows Server 2003 provide acceptable levels of performance in typical scenarios. However, on a high-latency connection, you may want to use an increased SizReqBuf value.

By default, all Windows 2000 and Windows 2003 Server installations use a SizReqBuf value of 16,644 bytes if the server has more than 512 megabytes (MB) of memory.

How to increase the SizReqBuf value

Important This section, method, or task contains steps that tell you how to modify the registry. However, serious problems might occur if you modify the registry incorrectly. Therefore, make sure that you follow these steps carefully. For added protection, back up the registry before you modify it. Then, you can restore the registry if a problem occurs. For more information about how to back up and restore the registry, click the following article number to view the article in the Microsoft Knowledge Base:
322756 How to back up and restore the registry in Windows

The SizReqBuf value is stored in the registry under the following registry key:

Value Name: SizReqBuf
Data Type : REG_DWORD
Data : 512 - 65535 (bytes in decimal, or 200 - FFFF hexadecimal)
Default : 4356 Specifies the size of request buffers that the server uses.

Note In Windows 2000 and Windows Server 2003, the minimum setting is 1024. Small buffers use less memory, and large buffers can improve performance. The exact value that works best in a particular environment depends on the specific configuration of that environment. For an optional value, try 4410 (hexadecimal); this has been shown to work well in a fairly standard Ethernet environment. By default, this setting is 4356 bytes on computers. On servers that have more than 512 MB of memory, this value is increased to 16 KB. A receive buffer that is larger can improve performance on query directory and similar commands, but at the price of more memory per work item.

Increasing the SizReqBuf value can increase performance significantly in a high-latency environment. However, note that increasing the SizReqBuf value also increases the non-paged pool memory that is used by the LanManServer service. If you increase the SizReqBuf value, monitor non-paged pool to make sure that the change does not affect the performance of the file server. Increasing the SizReqBuf value also proportionately increases the risk that a malicious user might exhaust non-paged pool on the file server.

Important Restart your computer after you change the registry value.