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Q152081: Use of Raw Data Transfer Mode Influenced by Application

Article: Q152081
Product(s): Microsoft Windows NT
Version(s): 3.1,3.5,3.51
Operating System(s): 
Keyword(s): kbnetwork
Last Modified: 19-FEB-2002

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The information in this article applies to:

- Microsoft Windows NT Server versions 3.1, 3.5, 3.51 
- Microsoft Windows NT Workstation versions 3.1, 3.5, 3.51 
- Microsoft Windows NT Advanced Server, version 3.1 
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SUMMARY
=======

There are several requirements that must be met for the Windows NT redirector to
use raw data transfer mode, which is considered to be a more efficient data
transfer mode than core mode. Applications can influence one or more of these
requirements in such a way that it is not immediately apparent why data transfer
is occurring in core mode and not raw mode.

MORE INFORMATION
================

The Windows NT redirector has the following requirements for performing raw mode
I/O, all of which must be satisfied for raw mode I/O to occur.

- The Server Message Block (SMB) protocol negotiated between the client and
  server must support raw mode.

- The server must be configured to support raw mode.

- The client redirector must be configured to allow raw mode.

- No other SMB requests are pending on the same Virtual Circuit (VC).

- The I/O is not on a blocking named pipe.

- For a READ request: the requested data size is equal to or greater than 2
  times the currently configured request buffer size, and the read offset is
  not past the redirector's currently configured end-of-file.

- For a WRITE request: the requested data size is equal to or greater than 1.5
  times the currently configured request buffer size, and the write offset is
  not more than approximately 1 MB past the current end-of-file.

- The I/O is to take no longer than 5 seconds to complete.

The above requirements are commonly satisfied, and it might be apparent that at a
given time raw I/O should be the data transfer mode of choice for the Windows NT
redirector. An application or process, however, might be causing the failure of
one or more of these requirements (and hence causing the redirector to use core
mode) in a subtle way that does not necessarily involve data passing on the VC.

An example of this is an application (such as File Manager) that posts a change
notification (for example, the FindFirstChangeNotification and
WaitForSingleObject or WaitForMultipleObjects APIs) which causes a long- term
pending SMB request(s) on the VC--even though no data is being actively passed
on the VC--and, hence, the failure of the requirement listed fourth above.

For more information on File Manager and change notification, please see the
following article in the Microsoft Knowledge Base:

Q123819File Manager I/O Optimizations Slow Other File Transfers

An application or process can also influence the redirector to use core mode
instead of raw mode by the size of its reads and writes (that is, reads smaller
than 2 times the currently configured request buffer size, or writes smaller
than 1.5 times the currently configured request buffer size) and the type of its
I/O (for example, on a blocking named pipe).

See your application vendor for more information if you suspect network
throughput performance problems are the direct result of an application
significantly influencing the data transfer mode as mentioned above.


Additional query words: throughput performance

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Keywords          : kbnetwork 
Technology        : kbWinNTsearch kbWinNTWsearch kbWinNT351search kbWinNT350search kbWinNTW350 kbWinNTW350search kbWinNTW351search kbWinNTW351 kbWinNTW310 kbWinNTSsearch kbWinNTS351 kbWinNTS350 kbWinNTS310 kbWinNTAdvSerSearch kbWinNTAdvServ310 kbWinNTS351search kbWinNTS350search kbWinNTS310search kbWinNT310Search kbWinNTW310Search
Version           : :3.1,3.5,3.51

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