Article ID: 842411 - View products that this article applies to.
A computer that is running Windows Server 2003 may not perform backup jobs to tape devices on a fiber or iSCSI storage area network (SAN), or backup performance may be severely affected.
This issue can also occur in a DPM environment in which more than one DPM server is sharing a tape library by using either a Fiber Channel switch or an iSCSI connection.
This issue may occur when a conflict exists between Plug and Play and another process on the computer. To check the status of a backup device, Plug and Play sends a Test Unit Ready request to the device every second. This request may conflict with other operations on the computer.
There are three methods to resolve this problem.
Method 1: Disable all Test Unit Ready (TUR) requests for a tape serviceImportant This section, method, or task contains steps that tell you how to modify the registry. However, serious problems might occur if you modify the registry incorrectly. Therefore, make sure that you follow these steps carefully. For added protection, back up the registry before you modify it. Then, you can restore the registry if a problem occurs. For more information about how to back up and restore the registry, click the following article number to view the article in the Microsoft Knowledge Base:
(http://support.microsoft.com/kb/322756/ )How to back up and restore the registry in Windows
Method 2: Disable TUR requests only for specific devices for a tape service
Note The quotation marks in this example are used only to show the correct use of fill spaces. The quotation marks are not used in the actual stored value. If the correct spacing is not used, TUR will not be disabled. You must restart the computer for this change to take effect.
[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\4MMdat\Enum] "0"="SCSI\Sequential&Ven_HP&Prod_C1537A&Rev_L907\5&347b98f7&0&060" [HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\4mmdat] REG_SZ:AutoRunAlwaysDisable:"HP C1537A "
Method 3: Disable TUR requests for specific devices programmaticallyTo programmatically disable TUR requests for specific devices, call the DeviceIoControl function with the IOCTL_STORAGE_MCN_CONTROL I/O control code. For more information, visit the following Microsoft Web site:
http://msdn2.microsoft.com/en-us/library/aa363415.aspxHP has documented a workaround that requires that you start and then stop the Removable Storage service every time that the server is restarted. This solution works because the Removable Storage service makes the DeviceIoControl function call to all tape devices when the service is stopped.
How to fix the Test Unit Ready request issue that affects Dell tape backup unit (TBU) devicesA conflict in Windows Server 2003 causes a Test Unit Ready (TUR) request issue on SCSI-attached, fiber-attached, or iSCSI-attached devices. When this issue occurs, an overflow of TUR requests causes the storage unit not to respond or to respond slowly to SCSI commands. In a fiber or iSCSI SAN environment, any Windows Server 2003-based computer that is zoned to detect the TBU hardware can send TUR requests. If you can see the devices in Device Manager on the server, the devices will send TUR requests even if drivers are not installed for the devices. You can use two methods to work around this issue. Method 1 is a temporary fix. Method 2 is applied to the registry. Method 2 is effective only until you change the driver files. If you change or upgrade the drivers, you must reapply this fix.
Method 1: Use the Removable Storage serviceYou can use the Removable Storage service to temporarily disable an overflow of TUR requests. To do this, enable the service. Then, start and stop the service. This method stops the TUR requests until the computer is restarted or until the driver is changed.
Note By default, the Removable Storage service is disabled.
To temporarily stop TUR requests, follow these steps:
Method 2: Modify the registry to disable TUR requests for TBU devicesTo use this method, find the driver files for the TBU devices. Then, configure settings for each of these driver files in the registry. You can use Device Manager to find the driver file for each TBU device. Device Manager also lists the Unknown Medium Changer driver.
To find the driver file details for the TBU devices, follow these steps:
Solution for Overland devicesOverland provides a workaround solution for the TUR request issue that you experience in Windows Server 2003. For more information about this workaround, visit the following Overland Web site:
http://support.overlandstorage.com/jive/entry.jspa?externalID=6561&categoryID=442The third-party products that this article discusses are manufactured by companies that are independent of Microsoft. Microsoft makes no warranty, implied or otherwise, about the performance or reliability of these products.
Article ID: 842411 - Last Review: May 13, 2011 - Revision: 11.0