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 policy

The 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:


Stand-alone instance

Clustered instance

SQL Server 2008



SQL Server 2008 R2



SQL Server 2012



SQL Server 2014



SQL Server 2016



SQL Server 2017 on Windows



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:

  • Mounted volumes

  • Mounted drives

  • Mountpoints

  • Mount points

  • Volume mount points

Stand-alone instance

On 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:

834661 SQL Server 2000 Setup requires a drive letter when you use mounted drives

Clustered instance

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:

  • SQL Server Setup requires that the base drive of a mounted drive has an associated drive letter. For failover cluster installations, this base drive must be a clustered drive. Volume GUIDs are not supported in this release.

  • The base drive is the drive that is assigned the drive letter. The base cannot be shared among failover cluster instances. This is a usual restriction for failover clusters but is not a restriction on stand-alone, multi-instance servers.

  • Be careful when you set up your failover cluster to make sure that both the base drive and the mounted disks or volumes are listed as resources in the resource group. SQL Server Setup validates drive configuration as part of a failover cluster installation.
    Note As a best practice, do not use the letters A or B for a cluster. However, this reduces the number of possible instance to 23 instances per cluster.

  • The SQL Server resource in SQL Server 2005 and later versions depends on the SQL network name resource and on the physical disk resources that hold the data. Mount points and the host drive must be displayed as a cluster physical disk resource. Additionally, the physical disk that has a drive letter and each mounted volume must also be added as a SQL Server dependency.

  • If you perform a new installation, the correct dependency permissions are set on the physical disks that have an associated drive letter and on the mount points. The dependency permissions are set automatically during setup.

Note To use this functionality, you must use a slipstreamed SQL Server 2008 or SQL Server 2008 R2 installation. This includes the cumulative update and the required service pack.

  • A SQL Server 2008 slipstream installation that includes SQL Server 2008 Service Pack 3 and cumulative update package 9 for SQL Server 2008 Service Pack 3.

  • A SQL Server 2008 R2 slipstream installation that includes the following:

    • SQL Server 2008 R2 Service Pack 1

    • Cumulative update package 10 for SQL Server 2008 R2 Service Pack 1

    • Cumulative update package 4 for SQL Server 2008 R2 SP2

  • A SQL Server 2012 installation that has Product Updates enabled and Cumulative Update Package 6 for SQL Server 2012 installed.

    Note The Product Updates feature in SQL Server 2012 requires Internet access to use the default source of Microsoft Update. You can also use local sources as noted in Installing SQL Server servicing Updates.

Important We recommend that you use the command line switches PCUSOURCE and CUSOURCE when you use a basic slipstream installation for SQL Server 2008 or SQL Server 2008R2. For SQL Server 2012 and SQL Server 2014, automatic updates during setup are recommended.

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.

More Information

  • X:\Program Files\Microsoft SQL Server\MSSQL10_50.InstanceID\Data
    Note This is the default path.

  • X:\Program Files\Microsoft SQL Server\MSSQL10_50.InstanceID\Log

  • Y:\Temp

  • Z:\MSSQL10_50.InstanceID\Backup


  • Z:\MountPoint1 is the container for mounted volumes.

  • Z:\MountPoint1\MP1 is the first mounted volume. When you install SQL Server, SQL Server Setup can be directed to a subfolder in a mounted folder. When you install SQL Server, you can specify the following:


  • Cluster Disk 1 has no required dependencies.

  • Cluster Disk 4, Mount point dependencies are Cluster Disk 1.

  • Cluster Disk 4, Mount point has no required dependencies.

  • IP Address: has no required dependencies.

  • IP Address: xxx:xxxx:c0:xxxx.xxxx:c597:8cb0:49f2 has no required dependencies.

  • Name: SOFTY dependencies are IP Address: xxx:xxxx:c0:xxxx:xxxx:c597:8cb0:49f2 and IP Address:

  • SQL Network Name (SOFTY) required dependencies are IP Address.

  • SQL Server dependencies are Name: SOFTY and Cluster Disk 4, Mountpoint and Cluster Disk 1.

  • SQL Server has no required dependencies.

Warning If you previously installed SQL Server to a root directory, you may be unable to install service packs or cumulative updates.DBCC CHECKDB


2867841 Permission error occurs when you use a volume mount point in SQLServer Setup

Cluster Shared Volumes (CSV)

Use Cluster Shared Volumes for SQL Server in a Failover Cluster prior to SQL Server 2014 is not supported.

Please refer to the following articles about using CSV with SQL Server 2014 or a later version:

Deploying SQL Server 2014 with Cluster Shared Volumes 

Cluster Shared Volumes

Use Cluster Shared Volumes in a Failover Cluster

Best practices when you use volume mount points

  • Create a dependency in the mounted volume disk resource that specifies the disk that is hosting the mount point folder. This makes the mounted volume dependent on the host volume, and it makes sure that the host volume comes online first.

    Note In Windows Server 2008 and later versions of Windows, this practice is no longer necessary.

  • If you move a mount point from one shared disk to another shared disk, make sure that the shared disks are located in the same group.

  • Try to use the root (host) volume exclusively for mount points. The root volume is the volume that hosts the mount points. This practice greatly reduces the time that is required to restore access to the mounted volumes if you have to run the Chkdsk.exe tool. This also reduces the time that is required to restore from backup on the host volume.

  • If you use the root (host) volume exclusively for mount points, the size of the host volume must be at least 5 megabytes (MB). This reduces the probability that the volume will be used for anything other than the mount points.


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

2216461 SQL Server 2008 setup fails to install on a Windows Server 2008-based cluster mount point

237701 Cacls.exe Cannot Apply Security to Root of a Volume Mount Point‎

2686690 FIX: SQL Server 2012 failover cluster installation takes an unexpectedly long time to validate clustered storage

2777358 SQL Server 2008 R2 Service Pack 1+Cumulative update package 4 for SQL Server 2008 R2 SP2

2783135 Cumulative update package 10 for SQL Server 2008 R2 Service Pack 1

280297 How to configure volume mount points on a Microsoft Cluster Server

2867841 Permission error occurs when you use a volume mount point in SQL Server Setup

835185 Failover cluster resource dependencies in SQL Server

878531 You cannot uninstall SQL Server 2012 that has dependencies on multiple mount points.

947021 How to configure volume mount points on a server cluster in Windows Server 2008

955392 How to update or slipstream an installation of SQL Server 2008

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 For more information about volume mount points, go to the following Microsoft website:

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:

  • "Windows Server 2012 Help"

  • "Disks and Data"

  • "Managing Disks and Data"

  • "Disk Management"

  • "Using NTFS Mounted Drives"

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