How do cluster shared volumes work

In contrast, in a failover cluster on which Cluster Shared Volumes is not enabled, a single disk LUN can only be accessed by a single node at a time. This means that clustered virtual machines can only fail over independently if each virtual machine has its own LUN, which makes the management of LUNs and clustered virtual machines more difficult. The following restrictions apply when using Cluster Shared Volumes in a failover cluster:. Toggle navigation. This topic contains the following sections: Benefits of using Cluster Shared Volumes in a failover cluster Restrictions on using Cluster Shared Volumes in a failover cluster Benefits of using Cluster Shared Volumes in a failover cluster Cluster Shared Volumes provides the following benefits in a failover cluster: The configuration of clustered virtual machines is much simpler than before.

For Cluster communication and heartbeats, there are several considerations that must be taken into account. Cluster communication between nodes is crucial so that all nodes are currently in sync. Cluster communication is constantly going on as things progress. The communications from the Cluster Service to other nodes through the NetFT adapter looks like this. Heartbeats are always traversing all Cluster enabled adapters and networks.

However, Cluster communication will only go through one network at a time. The network it will use is determined by the role of the network and the priority metric. Disabled for Cluster Communications — Role 0 - This is a network that Cluster will not use for anything. Enabled for Cluster Communication only — Role 1 — Internal Cluster Communication and Cluster Shared Volume traffic more later are using this type network as a priority.

Enabled for client and cluster communication — Role 3 — This network is used for all client access and Cluster communications. Cluster communication and Cluster Shared Volume traffic could use this network if all Role 1 networks are down. Based on the roles, the NetFT adapter will create metrics for priority.

A lower metric value means a higher priority while a higher metric value means a lower priority. I can run the following to see the metrics. Name Metric. Cluster Network 1 Cluster Network 2 In the example above, SMB Multichannel would not be used. But if there were additional cards in the machines and it looked like this:. Cluster Network 3 Cluster Network 4 Cluster Network 5 SMB Multichannel would fit nicely here so an additional network card or higher speed network cards are certainly a consideration.

In the beginning of the blog, I mentioned latency and packet loss. If heartbeats cannot get through in a timely fashion, node removals can happen. Heartbeats can be tuned in the case of higher latency networks. The following are default settings for tuning the Cluster networks. For more information on these settings, please refer to the Tuning Failover Cluster Network Thresholds blog. Planning networks for Failover Clustering is dependent on how it will be used. Clients are also connecting to the virtual machines.

Cluster Communications and heart beating will always be on the wire. If this was stretched nodes in multiple sites , you may have the need for an additional network as the considerations for replication such as Storage Replica traffic. As you can see, there is a lot of various network traffic requirements depending on the type of Cluster and the roles running. We do have a blog that will help with the Live Migration traffic to get some of the traffic isolated or limited in the bandwidth it uses.

I have already mentioned the Cluster specific networking considerations, but now I want to talk about how the virtual machines react in this type environment. As with most datacenters, they are in their own subnet and would be similar to this:.

The first thing you want to consider is if you want security between the cluster nodes on the wire. As a default, all Cluster communication is signed. That may be fine for some, but for others, they wish to have that extra level of security. We can set the Cluster to encrypt all traffic between the nodes.

It is simply a PowerShell command to change it. Upgrade to Microsoft Edge to take advantage of the latest features, security updates, and technical support. BitLocker Drive Encryption is a data protection feature that integrates with the operating system and addresses the threats of data theft or exposure from lost, stolen, or inadequately decommissioned computers.

The TPM is a hardware component installed in many newer computers by computer manufacturers. It works with BitLocker to help protect user data and to ensure that a computer hasn't been tampered with while the system was offline. On computers that don't have a TPM version 1.

However, this implementation will require the user to insert a USB startup key to start the computer or resume from hibernation. Starting with Windows 8, you can use an operating system volume password to protect the volume on a computer without TPM.

Neither option provides the pre-startup system integrity verification offered by BitLocker with a TPM. In addition to the TPM, BitLocker gives you the option to lock the normal startup process until the user supplies a personal identification number PIN or inserts a removable device. This device could be a USB flash drive, that contains a startup key. These additional security measures provide multi-factor authentication and assurance that the computer won't start or resume from hibernation until the correct PIN or startup key is presented.

However, the CSV drive will be in redirected mode which means write access will be sent to the coordinator node. With CSV, clustered roles can fail over quickly from one node to another without requiring a change in drive ownership, or dismounting and remounting a volume. CSV applications include:. BitLocker on volumes within a cluster are managed based on how the cluster service "views" the volume to be protected.

When using BitLocker with volumes designated for a cluster, the volume can be enabled with BitLocker before its addition to the cluster or when in the cluster. Put the resource into maintenance mode before enabling BitLocker.

Mount points are an NTFS object that is used to provide an entry point to other volumes. Mount points don't require the use of a drive letter. Volumes that lack drive letters don't appear in the BitLocker Control Panel item. BitLocker will unlock protected volumes without user intervention by attempting protectors in the following order:. Failover Cluster requires the Active Directory-based protector option for cluster disk resource.

This is a secure design because the protector is stored in Active Directory and protected by the CNO password. Also, it makes provisioning and unlocking volumes easy because every Failover Cluster node has access to the CNO account. This method obviously does not work when a Failover Cluster is created without any access to an Active Directory controller in the datacenter. Storage network. For storage network recommendations, review the guidelines that are provided by your storage vendor.

For additional considerations about storage for CSV, see Storage and disk configuration requirements later in this topic. For an overview of the hardware, network, and storage requirements for failover clusters, see Failover Clustering Hardware Requirements and Storage Options.

However, at any time, a single node called the coordinator node "owns" the physical disk resource that is associated with the LUN. Additionally, ownership is automatically rebalanced when there are conditions such as CSV failover, a node rejoins the cluster, you add a new node to the cluster, you restart a cluster node, or you start the failover cluster after it has been shut down.

When certain small changes occur in the file system on a CSV volume, this metadata must be synchronized on each of the physical nodes that access the LUN, not only on the single coordinator node. For example, when a virtual machine on a CSV volume is started, created, or deleted, or when a virtual machine is migrated, this information needs to be synchronized on each of the physical nodes that access the virtual machine.

These metadata update operations occur in parallel across the cluster networks by using SMB 3. These operations do not require all the physical nodes to communicate with the shared storage. File system format. Resource type in the cluster. By default, a disk or storage space that is added to cluster storage is automatically configured in this way.

Choice of CSV disks or other disks in cluster storage. When choosing one or more disks for a clustered virtual machine, consider how each disk will be used. If a disk will be a physical disk that is directly attached to the virtual machine also called a pass-through disk , you cannot choose a CSV disk, and you must choose from the other available disks in cluster storage.

Path name for identifying disks. Disks in CSV are identified with a path name. This path is the same when viewed from any node in the cluster.

You can rename the volumes if needed but is recommended done before any virtual machine if Hyper-V or application such as SQL Server is installed.

CSV cannot be renamed if there are any open handles i. For storage requirements for CSV, review the guidelines that are provided by your storage vendor. This section lists planning considerations and recommendations for using CSV in a failover cluster.

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. 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. 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. When you plan the storage configuration for a failover cluster that uses CSV, consider the following recommendations:.