How to Improve Data Transfers over RAS, RRAS, or Slow Links

In most instances, data transfer over a Remote Access Service (RAS) connection, or other forms of slow network links, is performed by the Windows NT redirector using core mode, because one of the redirector requirements for raw mode (that the I/O is to take no longer than 5 seconds to complete) is not satisfied. You can change this time limit requirement so that when all other requirements for raw mode are satisfied, data transfer over RAS or other slow links can be performed using raw mode.

You can configure the Windows NT redirector to accept a longer timeout period by changing the registry value (shown below) so that this requirement for raw mode might be more frequently satisfied when all other requirements are also satisfied. This should result in more frequent raw mode data transfers over RAS and other slow links.

WARNING: Using Registry Editor incorrectly can cause serious, system-wide problems that may require you to reinstall Windows NT to correct them. Microsoft cannot guarantee that any problems resulting from the use of Registry Editor can be solved. Use this tool at your own risk.

1. Start Registry Editor (Regedt32.exe).
2. Go to the following registry key:
   
   HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\Rdr\Parameters
3. If this value does not exist, you will need to add it using the following parameters:
   
   Value name: RawIoTimeLimit
   Data type: REG_DWORD
   Data range: 0-65535
   Default: 5 (seconds)
   
   NOTE: You must stop and restart the redirector, using the commands net stop rdr and net start rdr from a command prompt to put the new setting into effect.

The above registry value in place at a higher setting does not guarantee that data transfer will always occur using raw mode, because there are other requirements that must also be satisfied for the redirector to use raw mode.

For additional information, please see the following article in the Microsoft Knowledge Base:

152081  (http://support.microsoft.com/kb/152081/EN-US/ ) Use of Raw Data Transfer Mode Influenced by Application

The redirector locks the virtual circuit (VC) during raw I/O data transfers; therefore, all other pending I/O for that VC will not complete until after the current raw I/O is completed. In the case of large raw I/O (that is, a large file transfer with the above registry value in place at a higher setting) the result is significant performance degradation for other processes requiring access to the VC being used for the raw mode transfer.

Note that RRAS works on Windows NT 4.0 Server SP3 and later.