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 service

Important 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:

1. Click Start, click Run, type regedit, and then click OK.
2. Search in the
   \HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Enum
   registry subkey for all instances of the value class that equal TapeDrive.
3. In this subkey, a service value tells you what service handles the device. This
   Service_Name
   key is in the
   \HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services
   registry subkey. In the
   Service_Name
   key, you can use the
   Enum
   key to confirm the devices that are handled by this service.
4. Locate the subkey that corresponds to your storage device, and then right-click the subkey.
5. Point to New, and then click DWORD Value. Type AutoRun as the entry name, and then press ENTER.
6. Right-click AutoRun, and then click Modify. In the Value data box, type a value of 0 to turn off the AutoRun feature. 
   
   Key: \HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Service_Name
   Value: AutoRun 
   Type: REG_DWORD 
   Data: 0 is disabled, 1 is enabled (default).

Method 2: Disable TUR requests only for specific devices for a tape service

1. Follow steps 1 through 4 in method 1 to locate the tape service.
2. Set the REG_SZ AutoRunAlwaysDisable entry as follows. (Do not set the REG_DWORD AutoRun entry.)
   • The first 8 characters are the vendor ID. If the vendor ID is less than 8 characters, it is padded with spaces.
   • The second 16 characters are the product ID. If the product ID is less than 16 characters, it is padded with spaces.
   • If more than one device is added, the next device is appended to the previous device. 
     
     Key:
     \HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\<Service_Name>
     
     Entry: AutoRunAlwaysDisable
     Type: REG_SZ
     Data: The string to disable. This is the 8 character vendor ID string followed by the 16 character product ID.

In the following example, you see a correlation with the device under the Enum key: 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.

Method 3: Disable TUR requests for specific devices programmatically

To programmatically disable TUR requests for specific devices, call the DeviceIoControl function with theIOCTL_STORAGE_MCN_CONTROL I/O control code. For more information, visit the following Microsoft Web site: HP 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) devices

A 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 service

You 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:

1. Click Start, type services.msc, and then click OK.
2. In the right pane, double-click Removable Storage.
3. In the Startup type list, click Manual, and then click Apply.
4. Click Start, and then click Stop.
5. In the Startup type list, click Disabled, and then click OK.

Method 2: Modify the registry to disable TUR requests for TBU devices

To 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:

1. Click Start, type sysdm.cpl, and then click OK.
2. In the System Properties dialog box, click the Hardware tab.
3. Click Device Manager.
4. In the Device Manager window, right-click the TBU device, click Properties, and then click the Driver tab.
5. In the Driver tab, click Driver Details.
6. In the Driver File Details dialog box, note the driver file name.
7. Repeat steps 4 through 6 for all the TBU devices on the computer.

After you note the driver details for the TBU devices, configure settings for each of these driver files in the registry. To do this, follow these steps:

1. Click Start, type regedit, and then click OK.
2. In the left pane, locate and then click the following registry subkey:
   HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services
3. Expand the
   Services
   subkey, and then right-click the registry subkey that has the name of the driver file that you noted in Device Manager.
4. Point to New, and then click DWORD Value.
5. Type AutoRun, and then press ENTER.
6. Right-click AutoRun, and then click Modify.
7. In the Value data box, type 0 to turn off the AutoRun feature.
8. Repeat steps 3 through 7 for each driver file that you noted in Device Manager.
9. Exit Registry Editor, and then restart the computer.

Solution for Overland devices

Overland 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: The 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.