Cluster Shared Volumes
Encyclopedia
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
volume that is made accessible for read and write operations by all nodes within a Windows Server Failover Cluster. 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.
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.
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.
protocol. The node with ownership of the LUN orchestrating metadata updates to the NTFS volume is referred to as the Coordinator Node . 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.
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:
Import-Module FailoverClusters
Get-Cluster [-Name]| %($_.EnableSharedVolumes="Enabled")
Windows Server 2008 R2
Windows Server 2008 R2 is a server operating system produced by Microsoft. It was released to manufacturing on July 22, 2009 and launched on October 22, 2009. According to the Windows Server Team blog, the retail availability was September 14, 2009. It is built on Windows NT 6.1, the same core...
for use with the Hyper-V
Hyper-V
Microsoft Hyper-V, codenamed Viridian and formerly known as Windows Server Virtualization, is a hypervisor-based virtualization system for x86-64 systems. A beta version of Hyper-V was shipped with certain x86-64 editions of Windows Server 2008, and the finalized version was released on June 26,...
role. A Cluster Shared Volume is a shared disk containing an NTFS
NTFS
NTFS is the standard file system of Windows NT, including its later versions Windows 2000, Windows XP, Windows Server 2003, Windows Server 2008, Windows Vista, and Windows 7....
volume that is made accessible for read and write operations by all nodes within a Windows Server Failover Cluster. This enables a virtual machine
Virtual machine
A virtual machine is a "completely isolated guest operating system installation within a normal host operating system". Modern virtual machines are implemented with either software emulation or hardware virtualization or both together.-VM Definitions:A virtual machine is a software...
(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.
To use CSV, a Hyper-V VM is configured and the associated virtual hard disk
VHD (file format)
A Virtual Hard Disk is a virtual hard disk file format, meaning it can contain what is found on a physical hard disk drive, such as disk partitions and a file system, which in turn can contain files and folders. It is typically used as the hard disk of a virtual machine...
(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.
While CSV is not required for Live Migration
Live Migration
Live migration allows a server administrator to move a running virtual machine or application between different physical machines without disconnecting the client or application...
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.
Technical Details
Cluster Shared Volumes operates by orchestrating metadata I/O operations between the nodes in the cluster via the Server Message BlockServer Message Block
In computer networking, Server Message Block , also known as Common Internet File System operates as an application-layer network protocol mainly used to provide shared access to files, printers, serial ports, and miscellaneous communications between nodes on a network. It also provides an...
protocol. The node with ownership of the LUN orchestrating metadata updates to the NTFS volume is referred to as the Coordinator Node . Read / Write operations are passed directly to the Serial attached SCSI
Serial Attached SCSI
Serial Attached SCSI is a computer bus used to move data to and from computer storage devices such as hard drives and tape drives. SAS depends on a point-to-point serial protocol that replaces the parallel SCSI bus technology that first appeared in the mid 1980s in data centers and workstations,...
, iSCSI
ISCSI
In computing, iSCSI , is an abbreviation of Internet Small Computer System Interface, an Internet Protocol -based storage networking standard for linking data storage facilities. By carrying SCSI commands over IP networks, iSCSI is used to facilitate data transfers over intranets and to manage...
, Fibre Channel
Fibre Channel
Fibre Channel, or FC, is a gigabit-speed network technology primarily used for storage networking. Fibre Channel is standardized in the T11 Technical Committee of the InterNational Committee for Information Technology Standards , an American National Standards Institute –accredited standards...
, or Fibre Channel over Ethernet
Fibre Channel over Ethernet
Fibre Channel over Ethernet is an encapsulation of Fibre Channel frames over Ethernet networks. This allows Fibre Channel to use 10 Gigabit Ethernet networks while preserving the Fibre Channel protocol...
shared storage via block based protocols.
CSV builds a common global namespace across the cluster using NTFS reparse point
NTFS reparse point
An NTFS reparse point is a type of NTFS file system object. It is available with the NTFS v3.0 found in Windows 2000 or later versions. Reparse points provide a way to extend the NTFS filesystem by adding extra information to the directory entry, so a file system filter can interpret how the...
. 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:
Import-Module FailoverClusters
Get-Cluster [-Name
External links
- Step-by-Step (Microsoft Clustering & HA Team): http://blogs.msdn.com/clustering/archive/2009/02/19/9433146.aspx
- Step-by-Step (in English): http://www.servercare.nl/Lists/Posts/Post.aspx?ID=89
- Explained: How CSV works (in German): http://www.server-talk.eu/2009/09/15/einblicke-in-cluster-shared-volume-csv/
- EMC Symmetrix with Hyper-V (in English): http://www.emc.com/collateral/hardware/white-papers/h6643-symmetrix-microsoft-hyper-v-wp.pdf
- NetApp Storage Best Practices(in English): http://www.netapp.com/us/library/technical-reports/tr-3702.html