Microsoft KB Archive/248720

= PRB: Performance Hit in SCSI Miniport with Multiple Requests =

Article ID: 248720

Article Last Modified on 2/28/2007

-

APPLIES TO


 * Microsoft Windows 2000 Server
 * Microsoft Windows 2000 Advanced Server
 * Microsoft Windows 2000 Professional Edition

-



This article was previously published under Q248720



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:

260910 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:

276253 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.

