Drive letters are not automatically assigned to dynamic volumes in Windows Server 2003

This article describes a behavior in Microsoft Windows Server 2003 where a drive letter is not automatically assigned to a dynamic volume that you create or you mount.

When you create a new dynamic volume in Windows Server 2003, or when you mount a dynamic volume in Windows Server 2003, a drive letter is not automatically assigned to the volume. You must explicitly assign a drive letter to the volume.

This behavior occurs because in Windows Server 2003, the NO_DRIVELETTER volume attribute is set to Yes on all dynamic volumes. You cannot clear or set this attribute in Windows Server 2003.

The NO_DRIVELETTER attribute is set on dynamic volumes because the registry value does not affect dynamic volumes. Therefore, if the NO_DRIVELETTER attribute was not set for dynamic volumes, a dynamic volume would have a drive letter assigned when that volume was auto-mounted. This behavior would affect technologies such as storage area networks (SANs). The registry value does work for basic disks.

In Windows Server 2003, the NO_DRIVELETTER attribute is set as follows:

• On a dynamic volume, the NO_DRIVELETTER attribute is always set.
• For a GUID partition table (GPT) basic disk, the NO_DRIVELETTER attribute is set at the time of volume creation. This attribute is then turned on or off when drive letters are assigned to the volume or removed from the volume.
• For a master boot record (MBR) partition table basic disk, the NO_DRIVELETTER attribute is not set when the volume is created. However, in this scenario, a drive letter is not assigned to the volume because the Virtual Disk Service (VDS) removes the automatically-assigned drive letter when the VDS receives the volume device arrival notification from the Windows Plug and Play component.
  
  The NO_DRIVELETTER attribute is not turned on or off on a MBR basic disk when drive letters are assigned to the volume or removed from the volume. In this scenario, the NO_DRIVELETTER attribute is only changed when the SetFlags function or the ClearFlags function is called. The NO_DRIVELETTER attribute is applied to all the volumes on the hard disk at the next volume restart.
• For a MBR or GPT dynamic disk, NO_DRIVELETTER attribute is always set.

Microsoft Windows 2000 automatically assigns drive letters to dynamic volumes. However, the Windows code was changed in Windows Server 2003 and in Microsoft Windows XP so that Windows does not automatically assign drive letters to dynamic volumes. This code change is intended to improve support for storage area networks (SANs).

You can assign a drive letter to a volume by using the Disk Management snap-in in Windows Server 2003 or by using the diskpart command. For additional information about how to assign a drive letter in Windows Server 2003, visit the following Microsoft Web site:For additional information, visit the following Microsoft Web site: