Cluster Shared Volumes (CSV) is a feature of Failover Clustering first introduced in Windows Server 2008 R2 for use with the Hyper-V role. A Cluster Shared Volume is a shared disk containing an NTFS or ReFS (ReFS: Windows Server 2012 R2 or newer) volume that is made accessible for read and write operations by all nodes within a Windows Server Failover Cluster.
Cluster Shared Volumes (CSV) is a feature of Failover Clustering first introduced in Windows Server 2008 R2 for use with the Hyper-V role. A Cluster Shared Volume is a shared disk containing an NTFS or ReFS (ReFS: Windows Server 2012 R2 or newer) volume that is made accessible for read and write operations by all nodes within a Windows Server Failover Cluster.
Benefits[edit]
This enables a virtual machine (VM) complete mobility throughout the cluster as any node can access the VHD files on the shared volume. Cluster Shared Volumes simplifies storage management by allowing large numbers of VMs to be accessed off a common shared disk. CSV also increases the resiliency of the cluster by having I/O fault detection and recovery over alternate communication paths between the nodes in the cluster.
While CSV is not required for Live Migration of VMs, it reduces the potential disconnection period at the end of the migration since the NTFS file system does not have to be unmounted/mounted as is the case with a traditional cluster disk. This helps ensure seamless live migration since the physical disk resource does not need to be moved between nodes. CSV increases the chance that a live migration will complete within the TCP reconnect window and ensure a seamless operation to clients.
Requirements[edit]
To use CSV, a Hyper-V VM is configured and the associated virtual hard disk(s) are created on or copied to a CSV disk. Multiple VHDs can be placed on a CSV that in turn are associated with multiple VMs which can be running on different nodes in the cluster.
Technical Details[edit]
Cluster Shared Volumes operates by orchestrating metadata I/O operations between the nodes in the cluster via the Server Message Block protocol.[1] The node with ownership of the LUN orchestrating metadata updates to the NTFS volume is referred to as the Coordinator Node.[2] Read / Write operations are passed directly to the Serial attached SCSI, iSCSI, Fibre Channel, or Fibre Channel over Ethernet shared storage via block based protocols.
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CSV builds a common global namespace across the cluster using NTFS reparse point. Volumes are accessible under the %SystemDrive%ClusterStorage root directory from any node in the cluster.
The Cluster will automatically prioritize the most favorable network to route I/O operations by selecting the cluster shared network with the lowest cluster network metric value, this can also be manually configured. Public networks (i.e. networks that connect to users) are assigned higher cluster network metric values by default; this favors I/O operations from using the public network which may already be saturated with user requests.
CSV can be enabled in the Failover Cluster Manager MMC snap-in by selecting 'Enable Shared Volumes' from the information pane after creating a cluster. Additionally, CSV can be enabled using PowerShell:
References[edit]
External links[edit]
Retrieved from 'https://en.wikipedia.org/w/index.php?title=Cluster_Shared_Volumes&oldid=904912358'
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Applies to: Windows Server 2019, Windows Server 2016, Windows Server 2012, Windows Server 2012 R2
Cluster Shared Volumes (CSV) enable multiple nodes in a failover cluster to simultaneously have read-write access to the same LUN (disk) that is provisioned as an NTFS volume. (In Windows Server 2012 R2, the disk can be provisioned as NTFS or Resilient File System (ReFS).) With CSV, clustered roles can fail over quickly from one node to another node without requiring a change in drive ownership, or dismounting and remounting a volume. CSV also help simplify the management of a potentially large number of LUNs in a failover cluster.
CSV provide a general-purpose, clustered file system, which is layered above NTFS (or ReFS in Windows Server 2012 R2). CSV applications include:
Note
CSVs don't support the Microsoft SQL Server clustered workload in SQL Server 2012 and earlier versions of SQL Server.
In Windows Server 2012, CSV functionality was significantly enhanced. For example, dependencies on Active Directory Domain Services were removed. Support was added for the functional improvements in chkdsk, for interoperability with antivirus and backup applications, and for integration with general storage features such as BitLocker-encrypted volumes and Storage Spaces. For an overview of CSV functionality that was introduced in Windows Server 2012, see What's New in Failover Clustering in Windows Server 2012 [redirected].
Windows Server 2012 R2 introduces additional functionality, such as distributed CSV ownership, increased resiliency through availability of the Server service, greater flexibility in the amount of physical memory that you can allocate to CSV cache, better diagnosibility, and enhanced interoperability that includes support for ReFS and deduplication. For more information, see What's New in Failover Clustering.
Note
For information about using data deduplication on CSV for Virtual Desktop Infrastructure (VDI) scenarios, see the blog posts Deploying Data Deduplication for VDI storage in Windows Server 2012 R2 and Extending Data Deduplication to new workloads in Windows Server 2012 R2.
Review requirements and considerations for using CSV in a failover cluster
Before using CSV in a failover cluster, review the network, storage, and other requirements and considerations in this section.
Network configuration considerations
Consider the following when you configure the networks that support CSV.
For an overview of the hardware, network, and storage requirements for failover clusters, see Failover Clustering Hardware Requirements and Storage Options.
About I/O synchronization and I/O redirection in CSV communication
The server uses one of the following I/O redirection modes, depending on the situation:
In Windows Server 2012 R2, you can view the state of a CSV volume on a per node basis. For example, you can see whether I/O is direct or redirected, or whether the CSV volume is unavailable. If a CSV volume is in I/O redirected mode, you can also view the reason. Use the Windows PowerShell cmdlet Get-ClusterSharedVolumeState to view this information.
Note
Storage and disk configuration requirements
To use CSV, your storage and disks must meet the following requirements:
For storage requirements for CSV, review the guidelines that are provided by your storage vendor. For additional storage planning considerations for CSV, see Plan to use CSV in a failover cluster later in this topic.
Node requirements
To use CSV, your nodes must meet the following requirements:
Plan to use CSV in a failover cluster![]()
This section lists planning considerations and recommendations for using CSV in a failover cluster running Windows Server 2012 R2 or Windows Server 2012.
Important
Ask your storage vendor for recommendations about how to configure your specific storage unit for CSV. If the recommendations from the storage vendor differ from information in this topic, use the recommendations from the storage vendor.
Arrangement of LUNs, volumes, and VHD files
To make the best use of CSV to provide storage for clustered virtual machines, it is helpful to review how you would arrange the LUNs (disks) when you configure physical servers. When you configure the corresponding virtual machines, try to arrange the VHD files in a similar way.
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Consider a physical server for which you would organize the disks and files as follows:
For an equivalent clustered virtual machine, you should organize the volumes and files in a similar way:
If you add another virtual machine, where possible, you should keep the same arrangement for the VHDs on that virtual machine.
Number and size of LUNs and volumes
When you plan the storage configuration for a failover cluster that uses CSV, consider the following recommendations:
Add a disk to CSV on a failover cluster
The CSV feature is enabled by default in Failover Clustering. To add a disk to CSV, you must add a disk to the Available Storage group of the cluster (if it is not already added), and then add the disk to CSV on the cluster. You can use Failover Cluster Manager or the Failover Clusters Windows PowerShell cmdlets to perform these procedures.
Add a disk to Available Storage
Windows PowerShell equivalent commands (add a disk to Available Storage)
The following Windows PowerShell cmdlet or cmdlets perform the same function as the preceding procedure. Enter each cmdlet on a single line, even though they may appear word-wrapped across several lines here because of formatting constraints.
The following example identifies the disks that are ready to be added to the cluster, and then adds them to the Available Storage group.
Add a disk in Available Storage to CSV
Note
You can rename CSV volumes in the %SystemDisk%ClusterStorage folder.
Windows PowerShell equivalent commands (add a disk to CSV)
The following Windows PowerShell cmdlet or cmdlets perform the same function as the preceding procedure. Enter each cmdlet on a single line, even though they may appear word-wrapped across several lines here because of formatting constraints.
The following example adds Cluster Disk 1 in Available Storage to CSV on the local cluster.
Enable the CSV cache for read-intensive workloads (optional)
The CSV cache provides caching at the block level of read-only unbuffered I/O operations by allocating system memory (RAM) as a write-through cache. (Unbuffered I/O operations are not cached by the cache manager.) This can improve performance for applications such as Hyper-V, which conducts unbuffered I/O operations when accessing a VHD. The CSV cache can boost the performance of read requests without caching write requests. Enabling the CSV cache is also useful for Scale-Out File Server scenarios.
Note
We recommend that you enable the CSV cache for all clustered Hyper-V and Scale-Out File Server deployments.
By default in Windows Server 2012, the CSV cache is disabled. In Windows Server 2012 R2 and later, the CSV cache is enabled by default. However, you must still allocate the size of the block cache to reserve.
The following table describes the two configuration settings that control the CSV cache.
You can monitor the CSV cache in Performance Monitor by adding the counters under Cluster CSV Volume Cache.
Configure the CSV cache
Note
Backing up CSVsWindows Cluster Shared Volume 4
There are multiple methods to back up information that is stored on CSVs in a failover cluster. You can use a Microsoft backup application or a non-Microsoft application. In general, CSV do not impose special backup requirements beyond those for clustered storage formatted with NTFS or ReFS. CSV backups also do not disrupt other CSV storage operations.
You should consider the following factors when you select a backup application and backup schedule for CSV:
Important
Be sure to carefully review what data your backup application backs up and restores, which CSV features it supports, and the resource requirements for the application on each cluster node.
Warning
If you need to restore the backup data onto a CSV volume, be aware of the capabilities and limitations of the backup application to maintain and restore application-consistent data across the cluster nodes. For example, with some applications, if the CSV is restored on a node that is different from the node where the CSV volume was backed up, you might inadvertently overwrite important data about the application state on the node where the restore is taking place.
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