SQL Server support for mounted volumes

Support for Microsoft SQL Server 2000 data storage on mount points (also known as mounted drives, mounted volumes, or mount volumes) or on the very similar NTFS junction points varies, depending on whether an instance of SQL Server 2000 is a stand-alone instance or a clustered instance. A stand-alone instance does not use failover clustering. A clustered instance does use failover clustering. More information about each kind of instance follows. Later versions of SQL Server fully support mount points even on a cluster.

Stand-alone instance

On a stand-alone instance of SQL Server 2000, data storage on mount points is supported on Windows 2000, on Windows Server 2003, and on later versions. However, the SQL Server 2000 Setup program requires the base drive of a mounted drive to have an associated drive letter. If the base drive of a mounted drive does not have an associated drive letter, the Setup program will assign the next available drive letter to the drive. However, if all the drive letters are already assigned, the Setup program will fail.

For more information about how SQL Server requires a drive letter when you use mounted drives, click the following article number to view the article in the Microsoft Knowledge Base:

Clustered instance

On a clustered instance of SQL Server 2000, data storage on mount points is not supported. This applies to Windows 2000 and to Windows Server 2003 and later versions of Windows. The installation of SQL Server 2000 is not supported on a clustered configuration that has mount points even if the mount points are not meant to be used with the instance of SQL Server 2000. That is, if a configuration already has some mount points for file shares, you cannot install SQL Server 2000 on that configuration, even if you are not using the mount points for SQL Server 2000.

Failover clustered instances of SQL Server 2005 and of later versions fully support mount points if the mount point is hosted by a cluster drive that has a drive letter assigned, and if SQL Server depends on the mount point. SQL Server 2005 and later versions should not be installed to the root of the mount point but instead to subdirectories that are defined under the root.

Note Because of the number of available drive letters, the number of the virtual instances on a cluster is limited to 25. SQL Server 2005 and later versions have the same limitation. SQL Server supports use of mount points hosted only by drives that have drive letters that are not hosted by other mount points.

The SQL Server 2005 (and later-version) resource depends on the SQL network name resource and on the physical disk resources that hold its data. When mount points are being used together with the physical disks, each mount point must be displayed as a cluster resource. Additionally, each mount point must be added as a SQL Server dependency. If only the root physical disks dependency is added and the mount points are not added, database corruption will occur on failover. Database corruption may also occur when SQL Server is restarted without failing over.

A mount point is a volume or a drive that is mapped to a folder on a volume that uses the NTFS file system. Mounted drives function as any other volume or drive. A mounted drive is assigned a drive path instead of a drive letter.

Mount points are also known as "mounted volumes," as "mounted drives," as "mountpoints," or as "volume mount points." You can create mounted drives by using the Microsoft Windows 2000 Disk Management snap-in or by using the Mountvol.exe file.

Although mounted drives are a feature of Windows 2000, mounted drives are not supported on Windows 2000 cluster servers because of the failover behavior on Windows 2000 clustered servers for mounted drives and because of the assignment of different GUIDs for each disk on each node. The behavior of mounted volumes on a failover cluster was fixed for Windows Server 2003. Windows Server 2003 supports mounted drives in a cluster. However, because of limitations in SQL Server 2000, using mounted volumes on a clustered instance of SQL Server 2000 is not supported on any operating system.

A SQL Server 2000 installation is not supported on a clustered configuration with mounted drives because SQL Server 2000 was released before the mounted drive feature was released. The code that is used to enumerate the shared and the common local fixed disks in SQL Server 2000 in a clustered configuration is incompatible with mounted drives. This means that SQL Server 2000 cannot be installed on a cluster that contains mounted drives even if the instance of SQL Server 2000 does not use any of those mounted drives.

Because of similar limitations, an upgrade of a clustered instance of SQL Server 2000 is not supported if mount points exist on the cluster. An installation of SQL Server 2000 service packs on a clustered instance of SQL Server is also not supported if mount points exist.

Note The information in this article supersedes the information that is in the Microsoft Press book SQL Server 2000 High Availability that was published before this discovery. The information that is superseded appears in chapter 4, "Disk Configuration for High Availability," of part 2, "Microsoft SQL Server Technology."

For more information about mounted drives, click the following article numbers to view the articles in the Microsoft Knowledge Base:
For more information about volume mount points, visit the following Microsoft website:

For more information about mounted drives, see the following topics in Windows Help Online:

• "Windows Server 2003 Help"
• "Disks and Data" 
• "Managing Disks and Data"  
• "Disk Management" 
• "Using NTFS Mounted Drives"