Count the total number of physical cores in the server. Licensing for High Availability For each server licensed with SQL Server and covered by active SA, customers can run up to the same number of passive failover instances in a separate, on-premises OSE to support failover events. The passive failover instances can run on a separate server. These may only be used to synchronize with the primary server and otherwise maintain the passive database instance in a warm standby state in order to minimize downtime due to hardware or software failure.
But if Passive server hosted in cloud for failover, You need additional Licenses 3. Primary server licenses covered with SA include support for one secondary server only, and any additional secondary servers must be licensed for SQL Server. The rights to run a passive instance of SQL Server for failover support are not transferable to other licensed servers for purposes of providing multiple passive secondary servers to a single primary server.
Hope this is clear now when you need license for Passive Node. Cross Edition Rights are currently available for certain SQL Server products only and allow customers to deploy an alternate usually lower edition in place of the currently licensed edition. SQL Server cross edition rights can be combined with the version downgrade rights available for all products offered under a Volume Licensing Agreement that allow customers to deploy prior versions of the software in place of the currently licensed version.
In some cases, rights to deploy prior versions of product editions other than the edition currently licensed may also be allowed. How many minimum license required for core based licensed? Also screen shot: Leverages listener name for automatic application redirection.
Database Mirroring relies on modifying the application connection string to automatically redirect client applications to the mirror server upon failover. If the client application does not support the Failover Partner connection string parameter, you need to create a process that depends on DNS aliases for client application redirection after a failover.
An Availability Group listener name is a Windows Server Failover Clustering resource that resides in the same cluster resource group as the Availability Group. The listener name moves together with the Availability Group. Client applications simply need to use the listener name and they will always be redirected to the current primary replica. With Database Mirroring, you had to rely on a combination of the SQL Server error logs and the Windows Event logs to find out what caused a Database Mirroring configuration to go offline or failover unexpectedly.
However, both options still put you at a disadvantage — the former being at the risk of using an unmaintained feature, the latter being more expensive. This feature is not new and has been around since SQL Server 6. Highlighted below are the differences between the two that can help you make the right decision in choosing the appropriate high availability solution. While the comparisons apply to traditional Availability Groups as well, the focus will be on Basic Availability Groups.
A database is an object that resides within an instance. Understanding the difference between an instance and a database can help make decisions in implementing the appropriate high availability solution in terms of operational efficiency.
In an FCI, the entire instance is protected. If the primary node becomes unavailable, the entire instance is moved to the standby node. These instance-level objects are stored in the system databases which are physically stored in shared storage. In an Availability Group — be it the traditional or basic — only the databases in the group are protected. System databases cannot be added to an Availability Group — only user databases are allowed.
If all the dependent system objects are not replicated on all replicas, the database may end up becoming inaccessible to the application; as in the case of missing SQL Server logins or partially functional as in the case of missing certificates for Always Encrypted SQL Server Service Pack 1 made Always Encrypted available in Standard Edition.
If you are more concerned with instance-level protection to minimize possible human error during change management processes, then, an FCI is the way to go. Local storage versus shared storage An FCI requires some form of shared storage.
The shared storage is accessible to all of the nodes in the failover cluster but only the current primary node has ownership at any given point in time. The system and user databases are stored on the shared storage.
When a failover occurs, ownership of the shared storage moves from the current primary to the standby, making the databases available to the new primary node.
From a capacity point-of-view, you only need to provision disk space based on the sizes of the databases. However, from an availability point-of-view, the shared storage becomes a single point of failure. The FCI will remain offline if the shared storage becomes unavailable, regardless of the number of nodes in the failover cluster. An Availability Group does not require shared storage. Each replica has its own local storage independent of the Availability Group.
If the primary replica becomes unavailable and a failover occurs, any secondary replica can take over without having to rely on the availability of the system and user databases from the primary replica.
From a capacity point-of-view, you need to provision disk space based on the sizes of the databases and the number of secondary replicas, significantly increasing the cost per gigabyte. But from an availability point-of-view, because the Availability Group replicas do not rely on a single storage source, the SQL Server instance hosting the replicas remains online regardless of what happens to the primary replica.
Each Availability Group replica has its own copy of the system databases, thus, it is always online regardless of whether it is functioning as a primary or a secondary replica. The complexities of a shared storage subsystem like a storage area network SAN require the proper administration to guarantee high availability and resiliency because the storage becomes a single point of failure.
Single copy versus multiple copies You may have certain disaster recovery requirements to have multiple copies of your databases. If this is the case, then, Availability Group is your solution. Because of the shared storage requirement, an FCI will only have a single copy of the databases. If you need multiple copies of your databases, you will need to implement either log shipping, database mirroring or Availability Group together with the FCI.
This requires additional cost in terms of licensing and administrative overhead. Not so with Availability Groups. The standby server is only covered by a license if it comes with Software Assurance. Assume that you will only run a single instance FCI in a 2-node failover cluster and two replicas in a Basic Availability Group. One might think that a single Standard Edition license with Software Assurance will cover both servers. This is true in the case of an FCI.
Since you only have a single FCI, it can only be available on one of the failover cluster nodes at any given point in time. You cannot run the same FCI on all of the failover cluster nodes at the same time. In an FCI, the standby node acts as a true standby server. In an Availability Group, since all of the replicas are online and available at any given point in time, there is a possibility of running multiple Availability Groups simultaneously on any of the replicas.
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Many organizations will find this an attractive proposition, and in some circumstances, it is. However, there are a number of disadvantages and restrictions making it important to consider very carefully whether taking advantage of the VSDE route makes sense. Five reasons to take a chance It is free — although the commercially licensed version of SQL Server is often less expensive that other leading database products anyway, you cannot get it cheaper than for zero cost. While it may only be used for non-operational purposes, the developer edition is still a good way of trying out new functions, testing, training, and so on. It is fully loaded — it has all the same functions as the licensed SQL Server Enterprise edition, not a cut down version. This is important if you are using it to build applications that will eventually become real products or services.