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This article discusses issue that you must consider when you use mounted folders together with versions of Microsoft SQL Server in stand-alone and clustered environments.
Support policyThe availability of support for mounted folders depends on the version of SQL Server and on whether the instance of SQL Server is a stand-alone or clustered instance:
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Warning: SQL Server does not support use of mount volume / mount point root directories for SQL Server databases.
Note Mounted folders are also known as any of the following:
Stand-alone instanceOn a stand-alone instance of SQL Server, data storage on mount points is supported on currently supported versions of Windows Server and SQL Server. However, the SQL Server 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.
Note If all the drive letters are already assigned, the Setup program will fail.
For more information, click the following article number to view the article in the Microsoft Knowledge Base:
(https://support.microsoft.com/kb/834661/ )SQL Server 2000 Setup requires a drive letter when you use mounted drives
Clustered instanceOn a clustered instance of SQL Server 2000, data storage on mount points is not supported. 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.
On a failover clustered instance of SQL Server 2005 or in later versions of SQL Server, data storage on mount points is supported. However, the clustered installations of SQL Server are limited to the number of available drive letters. Therefore, if you use only one drive letter for the operating system, and if all other drive letters are available as normal cluster drives or as cluster drives that are hosting mount points, you are limited to no more than 25 instances of SQL Server per failover cluster.
A mounted volume, or mount point, lets you to use a single drive letter to refer to many disks or volumes. For example, if you have a drive letter R: that refers to a regular disk or volume, you can connect or "mount" additional disks or volumes as directories under drive letter R: without the additional disks or volumes requiring drive letters of their own.
Additional mount point considerations for SQL Server failover clustering include the following:
Important If you use a merged slipstream, that version of the slipstream must remain available in its original location as long as the instance of SQL Server exists.
Important You must manually set the correct dependencies in SQL Server 2005 and in versions of SQL Server 2008 Service Pack 2 and earlier versions. Additionally, you must set the correct dependencies in installations that are missing the required dependencies.
If only the root physical disks dependency is added and the mount points dependency is not added, database corruption will occur on failover. Database corruption may also occur during a SQL Server restart should disk resources go offline and return to online state even without failing over.
All currently supported versions of SQL Server and Windows Failover Clustering support mounted drives in a cluster.
The NTFS file system supports mounted folders. A mounted folder is an association between a volume and a directory on another volume. When a mounted folder is created, users and applications can access the target volume either by using the path of the mounted folder or by using the volume's drive letter. For example, a user can create a mounted folder to associate drive X: with the R:\Mnt\XDrive folder on drive R. After you create the mounted folder, the user can use the "R:\Mnt\XDrive" path of access drive X: as if it was a folder on the R: drive.
When you use mounted folders, you can unify different file systems such as the NTFS file system, a 16-bit FAT file system, and an ISO-9660 file system on a CD drive into one logical file system on a single NTFS volume. Neither users nor applications need information about the target volume on which a specific file is located. All the information that they must have to locate a specified file is a full path that uses a mounted folder on the NTFS volume. Volumes can be rearranged, substituted, or subdivided into many volumes without requiring users or applications to change settings.
Typically, SQL Server mounted folders use a single physical disk to host the mounted folders. The mount points are added by using descriptive folder names so that all the mounted folders are displayed as being on a single physical disk. This would apply to all disks that have mounted folders used with that instance of SQL Server.
In the following SQL Server 2008 R2 example, the drive letter could refer to either a local drive or a cluster disk:
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In this scenario:
The following is an example of a dependency report that shows a mount point that is being used:
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In this diagram:
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WarningIf you previously installed SQL Server to a root directory, you may be unable to install service packs or cumulative updates. We recommend that you create a folder, validate the current database integrity by using the DBCC CHECKDB statement, and then move the database to the folder that you created. For information about how to do this, go to one of the following Microsoft Developer Network (MSDN) websites:
Note: If you attempt to use the root drive to store a database you may be able to place the database there however this will prevent any type of upgrade from completing and produce errors as documented in the following KB article
(https://support.microsoft.com/kb/2867841/ )Permission error occurs when you use a volume mount point in SQLServer Setup
Best practices when you use volume mount pointsThe following are best practices when you use volume mount points:
For more information about mounted drives, click the following article numbers to view the articles in the Microsoft Knowledge Base:
(https://support.microsoft.com/kb/2216461/ )SQL Server 2008 setup fails to install on a Windows Server 2008-based cluster mount point
(https://support.microsoft.com/kb/237701/ )Cacls.exe Cannot Apply Security to Root of a Volume Mount Point
(https://support.microsoft.com/kb/2686690/ )FIX: SQL Server 2012 failover cluster installation takes an unexpectedly long time to validate clustered storage
(https://support.microsoft.com/kb/2777358/ )SQL Server 2008 R2 Service Pack 1+Cumulative update package 4 for SQL Server 2008 R2 SP2
(https://support.microsoft.com/kb/2783135/ )Cumulative update package 10 for SQL Server 2008 R2 Service Pack 1
(https://support.microsoft.com/kb/295732/ )How to create databases or change disk file locations on a shared cluster drive on which SQL Server 2000 was not originally installed
(https://support.microsoft.com/kb/832234/ )You cannot apply permissions to the root directory of an NTFS file system volume in Windows Server 2003
(https://support.microsoft.com/kb/835185/ )Failover cluster resource dependencies in SQL Server
(https://support.microsoft.com/kb/878531/ )You cannot uninstall SQL Server 2012 that has dependencies on multiple mount points.
(https://support.microsoft.com/kb/934012/ )Error message when you try to install SQL Server 2005 on a volume mount point: "There is not enough space on the destination disk for the current SQL Server installation"
(https://support.microsoft.com/kb/947021/ )How to configure volume mount points on a server cluster in Windows Server 2008
(https://support.microsoft.com/kb/955392/ )How to update or slipstream an installation of SQL Server 2008
956008For more information about volume mount points, go to the following Microsoft website:
(https://support.microsoft.com/kb/956008/ )After you install a SQL Server 2008 failover cluster in a disk that contains a mounted volume, no dependencies are created between the mounted volume and the disk
Mounted FoldersFor more information about the Product Update feature in SQL Server 2012, go to the following MSDN website:
Product Updates in SQL Server 2012 InstallationFor more information about mounted drives, see the following topics in Windows Help Online:
Article ID: 819546 - Last Review: September 29, 2015 - Revision: 28.0