Article ID: 310072 - View products that this article applies to.
This article was previously published under Q310072
Important This article contains information about how to modify the registry. Make sure to back up the registry before you modify it. Make sure that you know how to restore the registry if a problem occurs. For more information about how to back up, restore, and modify the registry, click the following article number to view the article in the Microsoft Knowledge Base:
(http://support.microsoft.com/kb/256986/ )Description of the Microsoft Windows registry
This article describes the support for a large number of logical unit numbers (LUNs) in Windows Server products. When you configure a server with more than eight LUNs, the hardware vendor must be involved in the planning and configuration. There may be several different ways to achieve the configuration you want; the hardware vendor is best equipped to supply the necessary information. This article is not meant to be all-inclusive because of the various implementations that a hardware vendor can use. Contact your hardware manufacturer to determine if and how your hardware can support more than eight LUNs. Windows Server products support up to:
Warning Serious problems might occur if you modify the registry incorrectly by using Registry Editor or by using another method. These problems might require that you reinstall your operating system. Microsoft cannot guarantee that these problems can be solved. Modify the registry at your own risk.
Terminology used in this article
Windows NT 4.0Large LUN support was added to Windows NT 4.0 Server in Service Pack 4 (SP4) and later service packs. This feature works only if the associated storage devices support the SCSI REPORT LUNS command. After you install SP4 or later, you may need to add the following registry value manually:
HKLM\SYSTEM\CurrentControlSet\Services\DriverName\Parameters\LargeLunsNote that DriverName is the name of the driver for which you want to enable Large LUN support. This causes all HBAs that are controlled by the specified driver to have Large LUNs enabled. Also note that "LargeLUNs" is plural. Microsoft recommends Windows NT 4.0 Service Pack 6a (SP6a) for Windows NT 4.0-based servers that use LargeLuns. For more information on issues with Windows NT 4.0 and LargeLun support, click the following article number to view the article in the Microsoft Knowledge Base:
The value should be a REG_DWORD value with a data value of 0x1.
(http://support.microsoft.com/kb/245637/ )Some LARGE LUN numbers are not available to the computer
Windows 2000 and laterWindows 2000 supports Large LUNs, but the method for enabling it depends on the hardware implementation and drivers. If the storage device reports the HiSupport bit in its standard inquiry data, Windows automatically enables Large LUNs without requiring any manual registry entries. Contact the hardware vendor to determine if the storage device reports the HiSupport bit. The hardware drivers may also enable large LUN support during their installation routines.
If the hardware does not report the HiSupport bit or the drivers do not enable Large LUN support, a manual registry entry is required. This feature works only if the storage devices support the SCSI REPORT LUNS command. Note that editing the registry to enable Large LUNs requires detailed knowledge of the devices' hardware IDs and registry entries; this is the least-preferred method. Please contact the hardware vendor for additional information. Follow these steps to configure the required registry entry:
Issues involved in manually enabling Large LUN supportDuplicate disks may appear after you enable Large LUN support. This can occur if the HBA driver enables Large LUN support in a proprietary fashion coupled with the manual registry entry. The issue occurs if both the Windows LargeLuns feature and the HBA's LargeLuns feature are enabled.
If logical unit 0 is not present, the REPORT LUNS command cannot be sent to the target device. Windows enumerates only eight logical units, even if more units are present in the disk array. To support large configurations, the time that is necessary to determine the size configuration needed to be minimized. Because the number of logical units can be as high as 255 on some systems, a lot of time can be spent in sending inquiry commands to non-existent logical units. Consult your hardware manufacturer about the different parameters that should be used with your particular hardware.
Even though Windows can access Large LUNs, there may be other environment variables that need to be taken into consideration. For more information, click the following article number to view the article in the Microsoft Knowledge Base:
277222For more information, click the following article number to view the article in the Microsoft Knowledge Base:
(http://support.microsoft.com/kb/277222/ )System may not start when creating a large number of logical units and volumes
(http://support.microsoft.com/kb/208173/ )Duplicate LUN 0 when LargeLuns registry key enabled
Additional parameters for the SpecialTargetList keyFor Windows 2000 and later, there are several additional parameters that you can use under the SpecialTargetList key. They are:
Article ID: 310072 - Last Review: March 1, 2007 - Revision: 4.3
Contact us for more help
Connect with Answer Desk for expert help.