DOCUMENT:Q248720  15-AUG-2002  [winnt]
TITLE   :PRB: Performance Hit in SCSI Miniport with Multiple Requests
PRODUCT :Microsoft Windows NT
PROD/VER::2000
OPER/SYS:
KEYWORDS:kbDDK kbOSWin2000bug kbOSWin2000fix kbStorageDev kbDSupport kbGrpDSNTDDK kbWin2000sp3fi

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The information in this article applies to:

 - Microsoft Windows 2000 Advanced Server 
 - Microsoft Windows 2000 Server 
 - Microsoft Windows 2000 Professional 
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SYMPTOMS
========

Windows 2000 SCSI miniport that sets the MultipleRequestPerLu member of the
PORT_CONFIGURATION_INFORMATION structure to TRUE, experiences performance hit.

CAUSE
=====

A SCSI Miniport that queues multiple requests per logical unit sets the
MultipleRequestPerLu member of the PORT_CONFIGURATION_INFORMATION structure to
TRUE. But this functionality has been disabled due the recent changes that were
made to the SCSIPORT driver. The code to implement this functionality was
affecting the drivers that did not request the multiple request functionality.

RESOLUTION
==========

To resolve this problem, obtain the latest service pack for Windows 2000. For
additional information, click the following article number to view the article
in the Microsoft Knowledge Base:

   Q260910 How to Obtain the Latest Windows 2000 Service Pack

For additional information about how to download the fix for this problem, click
the article number below to view the article in the Microsoft Knowledge Base:

   Q276253 Back-to-Back Queue Full Problem in Scsiport.sys

The English version of this fix should have the following file attributes or
later:

   Date          Time    Version         Size     File name
   -----------------------------------------------------------
   29-Nov-2001   15:11   5.0.2195.4702   73,296   Scsiport.sys

To work around this problem, you can claim that the miniport supports Tagged
Queuing. To do this, set the TaggedQueuing member of the
PORT_CONFIGURATION_INFORMATION structure for the controller.

If the driver is simulating a SCSI interface (as many RAID adapters do), it
should also set the CommandQueue bit in the Inquiry data that it generates. The
driver requires the Miniport to call ScsiPortNotification with the NextLuRequest
notification type at appropriate times. A genuine SCSI miniport should not
change the Inquiry data reported by the target devices.

STATUS
======

Microsoft has confirmed that this is a problem in Windows 2000. This problem was
first corrected in Windows 2000 Service Pack 3.

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

The Miniport developer can set the MultipleRequestPerLu member to whatever value
they want it to be, but it will be ignored by the current version of SCSIPORT
driver. However, this value will be taken by the new version that fixes this
problem.

The SCSIPORT driver always sets the MultipleRequestPerLu and TaggedQueuing member
to the value passed in the HW_INITIALIZATION_DATA structure when the miniport
driver calls ScsiPortInitialize.

REFERENCES
==========

Please refer the Windows 2000 DDK documentation for more information about
calling ScsiPortNotification and the other structures mentioned in this
article.


Additional query words: kbBaseOS SCSI scsiport miniport

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Keywords          : kbDDK kbOSWin2000bug kbOSWin2000fix kbStorageDev kbDSupport kbGrpDSNTDDK kbWin2000sp3fix 
Component         : DDK Drivers,SCSI
Technology        : kbwin2000AdvServ kbwin2000AdvServSearch kbwin2000Serv kbwin2000ServSearch kbwin2000Search kbwin2000ProSearch kbwin2000Pro kbWinAdvServSearch
Version           : :2000
Issue type        : kbbug
Solution Type     : kbfix

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