BUG: Duplicate LUN 0 When LargeLuns Registry Key Enabled

ID: Q208173

The information in this article applies to:
IMPORTANT: This article contains information about editing the registry. Before you edit the registry, make sure you understand how to restore it if a problem occurs. For information about how to do this, view the "Restoring the Registry" Help topic in Regedit.exe or the "Restoring a Registry Key" Help topic in Regedt32.exe.

SYMPTOMS

When the LargeLuns registry value is enabled for a SCSI adapter and the device supports the SCSI Report LUNs command, LUN 0 may incorrectly be reported multiple times.

For example, if Bus 0, Target ID (TID) 3, LUN 0 supports Report LUNs, IOCTL_SCSI_GET_INQUIRY_DATA might display information similar to this:

Bus TID LUN Claimed Inquiry String Unique or Duplicate
0 3 0 Y SEAGATE ST12550N Unique
0 3 0 Y SEAGATE ST12550N Duplicate
0 3 3 Y SEAGATE ST12550N Unique


CAUSE

The problem is caused by the way ScsiPort.sys parses the returned Report LUNs data. The driver incorrectly saves multiple structures representing LUN 0 internally, and this information is passed to the SCSI class drivers or applications via IOCTL_SCSI_GET_INQUIRY_DATA.


RESOLUTION

SCSI class drivers can be coded so they do not try to claim a device with a specific bus, target ID (TID), and logical unit number (LUN) more than one time. Duplicate entries returned by IOCTL_SCSI_GET_INQUIRY_DATA can be ignored.
To resolve this problem, obtain the latest service pack for Windows NT 4.0 or the individual fix. For information on obtaining the latest service pack, please go to:

For information on obtaining the individual fix, contact Microsoft Product Support Services. For a complete list of Microsoft Product Support Services phone numbers and information on support costs, please go to the following address on the World Wide Web:
http://www.microsoft.com/support/supportnet/overview/overview.asp

NOTE: If this product was already installed on your computer when you purchased it from the Original Equipment Manufacturer (OEM) and you need this fix, please call the Pay Per Incident number listed on the above Web site. If you contact Microsoft to obtain this fix, and if it is determined that you only require the fix you requested, no fee will be charged. However, if you request additional technical support, and if your no-charge technical support period has expired, or if you are not eligible for standard no-charge technical support, you may be charged a non-refundable fee.

For more information about eligibility for no-charge technical support, see the following article in the Microsoft Knowledge Base:
Q154871 Determining If You Are Eligible for No-Charge Technical Support


STATUS

Microsoft has confirmed this to be a problem in the Microsoft products listed at the beginning of this article. This problem was first corrected in Windows NT version 4.0 Service Pack 5.


MORE INFORMATION

WARNING: Using Registry Editor incorrectly can cause serious problems that may require you to reinstall your operating system. Microsoft cannot guarantee that problems resulting from the incorrect use of Registry Editor can be solved. Use Registry Editor at your own risk.

For information about how to edit the registry, view the "Changing Keys and Values" Help topic in Registry Editor (Regedit.exe) or the "Add and Delete Information in the Registry" and "Edit Registry Data" Help topics in Regedt32.exe. Note that you should back up the registry before you edit it. If you are running Windows NT, you should also update your Emergency Repair Disk (ERD).

With Windows NT 4.0 Service Pack 4, a new registry entry was added to support more than 8 logical unit numbers (LUNs). With this registry setting, up to 255 LUNs are supported. To enable this feature, the following registry value must be added to the system: 


HKEY_LOCAL_MACHINE\ 
  SYSTEM\ 
    CurrentControlSet\ 
      Services\ 
        Driver_Service_Key\ 
          Parameters\ 
            Device[Number]\

LargeLuns: REG_DWORD: 0x1

where Driver_Service_Key is the SCSI driver name and [Number] is the SCSI adapter number (0 for the first adapter, 1 for the second adapter, and so on) controlled by this specific driver.

If [Number] is not specified, this registry value will apply to all the adapters described by the Driver_Service_Key. To disable Large LUN support, either delete the LargeLun registry value or change the value to 0 (zero).

Additional query words: 


Keywords          : kbDDK kbNTOS400bug kbStorageDev nt4sp5fix 
Version           : winnt:4.0
Platform          : winnt 
Issue type        : kbbug

Last Reviewed: July 2, 1999