The communication between the nodes takes place through private network and each server are independent, making them standalone. For the better availability of Server database, storing in server clusters is recommended. Moreover, Clustering improves availability of physical server hardware, Server instances or even OS. Failover can be manually or automatically. Automatically indicates that the heartbeat of the server stopped. Manual has advantages, it is good when an event occurs that patches.
Clustering is profitable, if it is implemented, then when the hardware failure occurs, databases will be applicable for the applications which are dependent. An availability group listener on the primary replica's node responds to incoming client requests to connect to the virtual network name, and based on attributes in the connection string, it redirects each request to the appropriate SQL Server instance. In the event of a failover, instead of transferring ownership of shared physical resources to another node, WSFC is leveraged to reconfigure a secondary replica on another SQL Server instance to become the availability group's primary replica.
The availability group's virtual network name resource is then transferred to that instance. At any given moment, only a single SQL Server instance may host the primary replica of an availability group's databases, all associated secondary replicas must each reside on a separate instance, and each instance must reside on separate physical nodes.
A Failover Cluster Instance FCI may be used together with an availability group to enhance the availability of an availability replica. However, to prevent potential race conditions in the WSFC cluster, automatic failover of the availability group is not supported to or from an availability replica that is hosted on a FCI.
High availability for an Always On solution is accomplished though proactive health monitoring of physical and logical WSFC cluster resources, together with automatic failover onto and re-configuration of redundant hardware. A system administrator can also initiate a manual failover of an availability group or SQL Server instance from one node to another.
These policies, based on the severity, duration, and frequency of unhealthy cluster resource status and node responsiveness, can trigger a service restart or an automatic failover of cluster resources from one node to another, or can trigger the move of an availability group primary replica from one SQL Server instance to another.
Failover of an availability group replica does not affect the underlying SQL Server instance. Failover of a FCI moves the hosted availability group replicas with the instance. Each resource in a WSFC can report its status and health, periodically or on-demand. A variety of circumstances may indicate resource failure; e. WSFC resources such as networks, storage, or services can be made dependent upon one another. The cumulative health of a resource is determined by successively rolling up its health with the health of each of its resource dependencies.
Each node in a WSFC participates in periodic heartbeat communication to share the node's health status with the other nodes. Unresponsive nodes are considered to be in a failed state. If the WSFC has enough votes, it is healthy and able to provide node-level fault tolerance. A quorum mode is configured in the WSFC that dictates the methodology used for quorum voting and when to perform an automatic failover or take the cluster offline.
It is best practice to always have an odd number of quorum votes in a WSFC. For the purposes of quorum voting, SQL Server does not have to be installed on all nodes in the cluster. An additional server can act as a quorum member, or the WSFC quorum model can be configured to use a remote file share as a tie-breaker. Depending upon operational practices and WSFC configuration, you can incur both automatic and manual failovers, and still maintain a robust, fault-tolerant SQL Server Always On solution.
If the WSFC goes offline because of an unplanned disaster, or due to a persistent hardware or communications failure, then manual administrative intervention is required to force quorum and bring the surviving cluster nodes back online in a non-fault-tolerant configuration. Afterwards, a series of steps must also be taken to reconfigure the WSFC, recover the affected database replicas, and to re-establish a new quorum. A client request that specifies a logical availability group listener network name to connect to a primary or secondary database is redirected to the appropriate instance network name of the underlying SQL Server instance or SQL Server FCI.
SQL Server instances are actively hosted on a single node. Nodes are members of a WSFC cluster. WSFC configuration metadata and status for all nodes is stored on each node. Each server may provide asymmetric storage or shared storage SAN volumes for user or system databases. Each server has at least one physical network interface on one or more IP subnets.
Each prepared node must be the possible owner of at least one IP address. If each of the IP addresses specified for the subnets are supported on all the prepared nodes, the dependency is set to AND. If each of the IP addresses specified for the subnets are not supported on all the prepared nodes, the dependency is set to OR. Complete Failover Cluster requires that the underlying Windows Server failover cluster exists.
If the Windows Server failover cluster does not exist, Setup gives an error and exits. For more information about how to add nodes to or remove nodes from an existing failover cluster instance, see Add or Remove Nodes in an Always On Failover Cluster Instance Setup.
For more information about remote installation, see Supported Version and Edition Upgrades. Before Installing Failover Clustering.
You must have this information to create a new failover cluster instance. To install from a network share, browse to the root folder on the share, and then double-click Setup. For more information about how to install prerequisites, see Before Installing Failover Clustering. The System Configuration Checker runs a discovery operation on your computer. To continue, Click OK.. The System Configuration Checker verifies the system state of your computer before Setup continues. After the check is complete, select Next to continue.
On the Product key page, indicate whether you are installing a free edition of SQL Server, or whether you have a PID key for a production version of the product. On the License Terms page, read the license agreement, and then select the check box to accept the license terms and conditions. To help improve SQL Server, you can also enable the feature usage option and send reports to Microsoft. Select Next to continue. To end Setup, select Cancel.
On the Feature Selection page, select the components for your installation. A description for each component group appears in the right pane after you select the feature name. You can select any combination of check boxes, but only Database Engine, Analysis Services in tabular mode, and Analysis Services in multidimensional mode support failover clustering.
Other selected components will run as a stand-alone feature without failover capability on the current node that you are running Setup on. You cannot add features to a failover cluster instance after creation. For example, you cannot add the PolyBase feature to an existing failover cluster instance.
Make note of what features are needed before beginning the installation of a failover cluster instance. The prerequisites for the selected features are displayed on the right-hand pane. SQL Server Setup will install the prerequisite that are not already installed during the installation step described later in this procedure. You can specify a custom directory for shared components by using the field at the bottom of this page. To change the installation path for shared components, either update the path in the field provided at the bottom of the dialog box, or select the ellipsis button to browse to an installation directory.
The path specified for the shared components must be an absolute path. The folder must not be compressed or encrypted. Mapped drives are not supported. If you are installing SQL Server on a bit operating system, you will see the following options:. When you select the Database Engine Services feature, both replication and full-text search are selected automatically.
Unselecting any of these subfeatures also unselects the Database Engine Services feature. SQL Server setup runs one more set of rules that are based on the features you selected to validate your configuration. On the Instance Configuration page, specify whether to install a default or a named instance. For more information, see Instance Configuration. This is the name that is used to identify your failover cluster instance on the network.
This is used to identify installation directories and registry keys for your instance of SQL Server. This is the case for default instances and named instances. Typical stand-alone instances of SQL Server, whether default or named instances, do not use a nondefault value for the Instance ID box.
To specify a nondefault root directory, use the field provided, or select the ellipsis button to locate an installation folder. If a default instance is already installed on the computer, you must install a named instance of SQL Server. Use the Cluster Resource Group page to specify the cluster resource group, or role, name where SQL Server virtual server resources will be located.
To specify the SQL Server cluster resource group name, you have two options:. Type the name of a new group to create.
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