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If you created the following types of volumes in Windows NT 4.0, these volumes are no longer accessible after you upgrade from Windows NT Server 4.0 to Windows Server 2003:
Spanned volume sets
Striped volumes with parity (RAID 5)
The Disk Management utility may indicate that these volumes have "Healthy (Unknown Partition)" status, but the listing may not have an associated drive letter.
NOTE: This behavior may also occur on disks that you have moved from a Windows 2000-based computer to a Windows Server 2003-based computer that contain previous fault-tolerant sets on BASIC disks.
Additionally, the list volume command in the Diskpart command-line utility does not display these volumes.
This behavior occurs because Windows Server 2003 does not support all previous Windows NT 4.0 fault-tolerant disk (FTDisk) volumes.
To temporarily mount the data on these volumes for recovery purposes, you can use the FTOnline utility (Ftonline.exe) from the Windows Server 2003 Support Tools, which is located in the Support\Tools folder on the Windows installation media. To install the support tools to your hard disk, either run the Suptools.msi package or extract Ftonline.exe manually from the Support.cab file.
To use FTOnline, run the following command from a command prompt, where drive is the drive letter of the previous Windows NT 4.0 FTDisk volume that you want to bring online:
Because the drive letters that are assigned to FTDisk volumes are not displayed in the Disk Management console (or in Diskpart), you may have to run the mountvol command with no arguments to determine which drive letters are assigned on the computer. Any drive letters that are listed by mountvol but are not displayed in the Disk Management console are typically FTDisk volumes.
When FTOnline brings a previous FTDisk volume online, you have full access to that volume for the duration of the Windows session. After you restart the computer, the volume is inaccessible until you run FTOnline on that volume again.
This behavior is by design.
When you use the FTonline utility, you have temporary access to data on previous Windows NT 4.0 FTDisk volumes so that you can back up the data. The Ftonline utility is not designed to provide persistent support for previous FTDisk volumes in Windows Server 2003.
FTOnline does not support breaking mirrors, repairing failed RAID-5 sets, or performing other maintenance functions on previous FTDisk volumes.
After you bring your previous FTDisk volumes online by using FTOnline, Microsoft recommends that you back up the data on those volumes, and then delete them. You can then convert the disks to Dynamic disks, re-create the volumes, and then restore the data.