Windows NT Cannot Regenerate Stripe Set with Parity

• Microsoft Windows NT Advanced Server version 3.1

SYMPTOMS

If you remove a drive from a stripe set with parity, deleting a stripe partition on another computer, when you reinsert the drive back into the stripe set with parity, the stripe set with parity is not allowed to regenerate.

CAUSE

Windows NT places a unique identifier on all drives it uses. When it sees the identifier previously used in the stripe set with parity, it does not detect the modifications made to the drive and is misled about the state of the configuration. Windows NT is not changing this identifier when partitions are deleted.

In normal production environments, this situation should not be encountered. A failed drive is usually replaced with a different one. Even if a drive is repaired, it is usually low-level formatted in the process unless a specific request is made to save the data if possible. The low- level format should remove the identifier Windows NT placed on the drive.

The most likely situation where this issue may be seen is in a pre- production testing environment prior to Windows NT implementation. For example, the tester, wanting to simulate a drive failure, pulls a good drive out of the system while it is running. Not having an additional drive available to replace it with, the tester takes the drive to a different machine and removes the partitions thinking that this will simulate a new drive.

Another possibility for causing this would be if a hardware hot-swapable drive array was not configured in a way to present the array of drives to the operating system as one drive. In this situation, Windows NT would have to detect and automatically process a drive that was hot-swapped. This feature is not available as a part of Windows NT Fault Tolerance. For this kind of Fault Tolerance to be used, it has to be implemented at the hardware level.

RESOLUTION

To work around this problem, do the following:

If this kind of testing is going to be done, either use a different drive for replacement or delete the information kept in sector zero of the drive. A different disk, even if previously used under Windows NT, will contain a different identifier. This difference will be correctly detected by Windows NT Fault Tolerance and regeneration of the stripe with parity set will be possible. A low-level format should remove sector zero information, or a disk editor program could be used.

If a drive is repaired and a request is made to save the data, make a tape backup of the recovered data on the drive. Use the above techniques to remove the Windows NT identifier before you attempt to reuse the drive in the Windows NT computer.

Warnings

Although techniques such as pulling a drive out of a system while it is running may be used in testing, they do result in a degree of risk. Microsoft does not recommend the use of these techniques and will not be responsible for any negative consequences of doing so.

Mention of the identifier in sector zero as an implementation detail of Windows NT Fault Tolerance is only for the purpose of clarifying why partition removal is an inadequate procedure. Microsoft does not support the non-Microsoft use of this information. This implementation detail may be modified or removed at any time if Microsoft deems it to be appropriate to do so. Microsoft specifically rejects any claim to product support arising out of the access or use of this implementation detail by a non- Microsoft process.

STATUS

Microsoft has confirmed this to be a problem in Windows NT Advanced Server version 3.1. We are researching this problem and will post new information here in the Microsoft Knowledge Base as it becomes available.

MORE INFORMATION

Steps to Reproduce Problem

1. Use Disk Administrator to set up a stripe with parity set.

2. While Windows NT is running, disconnect one drive of the stripe set with parity to simulate a drive failure.

3. Shut down the computer with stripe set with parity.

4. Take the disconnected drive to another computer and remove all partitions on it in an attempt to simulate a new drive.

5. Place the disconnected drive back in the stripe set with parity computer.

6. Boot Windows NT, log on, then start Disk Administrator.

7. Select the stripe with parity set, press the CTRL key and select the previously disconnected drive.

8. Select Fault Tolerance.