What is Availability Group in SQL Server<\/h2>\n
SQL Server Always On Availability Groups is based on Mirroring Technology.\u00a0 Moreover, Availability Group is improved version of Mirroring.<\/p>\n
You may want to read my article “Database Mirroring On SQL Server<\/a>“.<\/p>\n SQL Server AlwaysOn Availability Groups can be HA (High Availability) and DR (Disaster Recovery) solution.<\/p>\n If you want to use Availability Group as the HA solution, you need more than one server in the same data center.<\/p>\n As a DR solution, you can use this technology by adding another secondary server in different locations.<\/p>\n You can use Availability Groups as DR by locating primary and secondary server at different data centers. If the primary data center becomes completely unserviceable(earthquake, flood, fire), you can use secondary database on secodary data center. For example, if your data center is located in a city named A, you can choose B as a disaster center or a less risky city.<\/p>\n To install Availability Group, you need at least 2 servers that must be in the same windows cluster. Availability Group provides HA and DR solutions with AG (Availability Group).<\/p>\n\n SQL Server 2016 supporys Distributed Transaction for Availability Groups. Its called Distributed Availability Group.<\/p>\n However, it is not supported if there are multiple databases associated with the transaction on the same instance. When creating the Availability Group, we need to create it by adding WITH DTC_SUPPORT = PER_DB. In addition, the operating system must be a minimum of Windows Server 2012 R2 and the KB3090973 patch needs to be installed.<\/p>\n Remember, we can use Database Mirroring database basis. So if you want to add more than one databases for Mirroring you must seperately configure them.<\/p>\n But, we can add more than one database to an availability group. Failover is performed on an Availability Group basis. For example, you have 50 databases on your instance. You have created 5 Availability Groups for this 50 database. You can actively operate 3 of these 5 Availability Groups in the 1st server and 2 of these 5 in the 2nd server.<\/p>\n Or you can change the availability groups primary server by performing failover at any time you want. It is easier for us to manage this process with Availability Group.<\/p>\n And we can set availability group secondary as readonly. In mirroring we must use database snapshot to read from secondary.<\/p>\n You can read my article “Readable\u00a0 Secondary On SQL Server Always On Availability Group<\/a>” to be able to read from the secondary database on Availability Group.<\/p>\n As in Mirroring, there are Synchronous and Asynchronous databases. On the basis of AG, you can set synchronous or asynchronous.<\/p>\n If you set AG synchronously, all databases in AG will work synchronously. When user requests come to the primary database, transaction completion information is passed to the user after the operation is reflected on the secondary server.<\/p>\n This may cause some performance loss in very heavily transactional databases.<\/p>\n But, automatic failover is possible if we use synchronous availability groups. In the event of any problems with the servers, the AG will continue to serve automatically from the other server without anyone being aware of it.<\/p>\n If you set AG asynchronously, when user requests come to the primary database, transaction completion information is passed to the user before the operation is reflected on the secondary server.<\/p>\n The question always asked is: If we set to AG asynchronous, how far behind the secondary databases? There is no period. This time depends on the performance of the existing hardware and network. But it’s usually a few seconds.<\/p>\n\n You can set automatic or manual failover on the basis of AG. You need to set the AG synchronously to perform automatic failover. As long as I don’t see HADR_COMMIT waiting, I set Ag synchronously and automatically.<\/p>\n As the performance loss is more when rebilding indexes, I set asynchronously the AG before Index Rebuild in the systems that are experiencing distress.<\/p>\n The automatic failover process does not occur as a result of an error in a database that is included in the AG.<\/p>\n Failover operation does not occur in the following cases;<\/p>\n Let me give you an example to explain how HA and DR are used in Availability Group.<\/p>\n You have 2 servers in your data center. These two servers have made a windows cluster. You have set up Availability Group running synchronously on these two servers. This is an HA (High Availability) solution.<\/p>\n We have a server in your data center in another city. You have included this third server in your existing windows cluster.<\/p>\n Note:<\/strong>If you dont want to add third server to your windows cluster you can use it still. Only you need to do is creating availability group with CLUSTER_TYPE=NONE<\/strong>.<\/p>\n Then add the database on the disaster recovery center as asynchronous to the existing Availability Group. This process is called DR (Disaster Recovery) solution. On Availability Group we can make multiple secondary for the same AG.<\/p>\n Now let’s start the install Always On AG Availability Group for the HA solution.<\/p>\n \u2022 You must have 2 servers included in the same windows cluster. You can request it from your system group or install it yourself.<\/p>\n \u2022 You need to install SQL Server as stand-alone on these 2 servers. You can find detailed information in my article “How To Install SQL Server<\/a>“.<\/p>\n \u2022 Set the service accounts of the stand-alone instances that you have installed on these 2 servers to the same domain user. For example, [mydomain\\myuser]. You can read the article “SQL Server Configuration Manager Settings<\/a>” to change service accounts.<\/p>\n \u2022 The Windows Cluster Account (Windows Cluster’s name) installed on these 2 servers needs to be granted the Create Computer Object privilege in the OU (Organization Unit) where these 2 servers reside in Active Directory. You should talk with the Active Directory team in your organization and create an OU for your SQL Server Servers. After you create the OU, you must also specify the policies to be applied to this OU. You can article links about policies at the end of the section.<\/p>\n If you do not grant Create Computer Object permission to Windows Cluster, you will get an error as below when creating a listener.<\/p>\n The WSFC cluster could not bring the Network Name resource with DNS name ‘testAG’ online. The DNS name may have been taken or have a conflict with existing name services, or the WSFC cluster service may not be running or may be inaccessible. Use a different DNS name to resolve name conflicts, or check the WSFC cluster log for more information.<\/em><\/span><\/p>\n The attempt to create the network name and IP address for the listener failed. The WSFC service may not be running or may be inaccessible in its current state, or the values provided for the network name and IP address may be incorrect. Check the state of the WSFC cluster and validate the network name and IP address with the network administrator. (Microsoft SQL Server, Error: 19471)<\/em><\/span><\/p>\n \u2022 Databases you want to add to the AG must be in the full recovery model.<\/p>\n \u2022 Database full backup is required. If you have a full backup after you have taken the database to Full Recovery Model, you do not need to backup again.<\/p>\n I recommend you read my articles about policies.<\/p>\n “SQL Server Account Lockout Policy<\/a>“,<\/p>\n “Security Policy for SQL Server(secpol.msc)<\/a>“,<\/p>\n “SQL Server Password Policy<\/a>“,<\/p>\n “How To Create a Login On SQL Server(Manage Logins)<\/a>”<\/p>\n Once we have completed the above mentioned preparations, we can proceed to the creation of the AG.<\/p>\n\n First, we need to enable Always ON\u00a0Availability Group on two instances. If you do not activate, you will receive an error as follows.<\/p>\n The AlwaysOn feature must be enabled for the server instance ” before you can create an availability group on this instance..<\/em><\/span><\/p>\n To enable Always On Availability Group, we open SQL Server Configuration Manager with Run As Administrator. In SQL Server Services, we right-click on the instance and click properties.<\/p>\n In the tab that opens, select AlwaysOn High Availability, click Enable AlwaysOn Availability Groups and click OK to activate Always On Availability Group. We need to perform this process on the two servers for Always On Availability Group. This will require a service restart. You can restart your sql server services in a controlled manner.<\/p>\n After enabling Always On Availability Group in two servers, we click New Availability Wizard from AlwaysOn High Availability on SSMS as follows.<\/p>\n We need to give a name to AG in the incoming screen. Our AG’s name is IlkAG. We’re moving forward by clicking next.<\/p>\n In the incoming screen, we select the databases that we will add to AG. The status of the databases that are suitable for receiving AG appears in the form of “Meets prerequisities”. We’re choosing TestDB.<\/p>\n On the next screen, in the Replicas section, click Add to connect to the second instance of Availability Group. Make sure that the instance names are the same. For example, if your primary server is “Server1\\Instance1”, your secondary server should be “Server2\\Instance1”. In other words, the name of the named instance on both servers is Instance1.<\/p>\n After the connection is complete, you should see a screen as follows.<\/p>\n Since we want to set the AG to be synchronous and automatic failover, we mark the required fields as follows.<\/p>\n For now, we leave Readable Seconday as “No”.<\/p>\n You can read my article “Readable\u00a0 Secondary On SQL Server Always On Availability Group<\/a>” to be able to read from the secondary database on Availability Group.<\/p>\n\n After performing the operations on the Replicas tab, we switch to the Endpoints tab and a screen like the one below is displayed.<\/p>\n To set Always On Availability Group, if you use more than one instance on the same server, you will need to use a different endpoint port for each instance. The default endpoint port is 5022.<\/p>\n For example, you have 3 instances. When creating the availability group for the first instance, the default port is 5022. You must change the port from the Enpoint URL when you create a availability group for your second instance. You can use 5023 for the second instance and 5024 for the third instance. We will use port 5023 for the instance in our example.<\/p>\n We go to the Backup Preferences tab and see a screen like the following. This screen asks for the preferred instance to create backups. You must choose one of them.<\/p>\nWhat is Distributed Availability Group?<\/h3>\n
![](\"https:\/\/dbtut.com\/wp-content\/uploads\/2018\/10\/709.png\")
<\/p>\nWhat is the difference between database mirroring and alwayson availability groups<\/h3>\n
SQL Server Availability Groups synchronous vs asynchronous<\/h3>\n
SQL Server Availability Group Automatic Failover<\/h3>\n
Alwayson Automatic Failover not working?<\/h4>\n
\n
SQL Server Availability Group HA or DR?<\/h3>\n
SQL Server Always On Requirements<\/h3>\n
Hardware and Installation Requirements:<\/h4>\n
Permission Reqirements:<\/h4>\n
Database based Requirements:<\/h4>\n
SQL Server Policy Articles<\/h4>\n
SQL Server Always On Availability Groups Step by Step<\/h2>\n
Enable Always On Availability Groups<\/h3>\n
![](\"https:\/\/dbtut.com\/wp-content\/uploads\/2018\/10\/372.png\")
<\/p>\n![](\"https:\/\/dbtut.com\/wp-content\/uploads\/2018\/10\/576.png\")
<\/p>\n![](\"https:\/\/dbtut.com\/wp-content\/uploads\/2018\/10\/827.png\")
<\/p>\nCreate Always On Availability Group<\/h3>\n
![](\"https:\/\/dbtut.com\/wp-content\/uploads\/2018\/10\/351.png\")
<\/p>\n![](\"https:\/\/dbtut.com\/wp-content\/uploads\/2018\/10\/631-1.png\")
<\/p>\n![](\"https:\/\/dbtut.com\/wp-content\/uploads\/2018\/10\/559.png\")
<\/p>\n![](\"https:\/\/dbtut.com\/wp-content\/uploads\/2018\/10\/761-1.png\")
<\/p>\n![](\"https:\/\/dbtut.com\/wp-content\/uploads\/2018\/10\/165.png\")
<\/p>\nCreate Endpoint in SQL Server Availability Group<\/h3>\n
![](\"https:\/\/dbtut.com\/wp-content\/uploads\/2018\/10\/762.png\")
<\/p>\nChange Endpoint url Availability Group<\/h3>\n
Availability Group Backup Preferences<\/h3>\n
![](\"https:\/\/dbtut.com\/wp-content\/uploads\/2018\/10\/249.png\")
<\/p>\n![](\"https:\/\/dbtut.com\/wp-content\/uploads\/2018\/10\/988-1.png\")
<\/p>\n![](\"https:\/\/dbtut.com\/wp-content\/uploads\/2018\/10\/168.png\")
<\/p>\n![](\"https:\/\/dbtut.com\/wp-content\/uploads\/2018\/10\/827-1.png\")
<\/p>\n![](\"https:\/\/dbtut.com\/wp-content\/uploads\/2018\/10\/392-1.png\")
<\/p>\n![](\"https:\/\/dbtut.com\/wp-content\/uploads\/2018\/10\/771.png\")
<\/p>\n![](\"https:\/\/dbtut.com\/wp-content\/uploads\/2018\/10\/921.png\")
<\/p>\n![](\"https:\/\/dbtut.com\/wp-content\/uploads\/2018\/10\/702.png\")
<\/p>\n