Microsoft SQL Server log shipping on existing AlwaysOn databases
This post discusses how to set up log shipping, which is a disaster recovery (DR) solution, with existing Microsoft® SQL Server® AlwaysOn-configured databases.
The AlwaysOn availability group (AG) feature is a high-availability and disaster recovery solution that provides an enterprise-level alternative to database mirroring. Introduced in SQL Server 2012 (11.x), AlwaysOn AGs maximize the availability of a set of user databases for an enterprise. AGs support a fail over environment for a discrete set of user databases, known as availability databases, that fail over together. They also support a set of read-write primary databases and one to eight sets of corresponding secondary databases. Optionally, AGs can make secondary databases available for read-only access and some backup operations.
SQL Server log shipping enables you to automatically send transaction log backups from a primary database on a primary server instance to one or more secondary databases on separate secondary server instances. The transaction log backups are applied to each of the secondary databases individually.
Reasons why you might need AlwaysOn log shipping
Let's assume that you have configured an AlwaysOn setup between your primary replica server and your secondary replica and that AlwaysOn is used in the main data center. You might need to use log shipping if you can’t expand the required Windows Server Failover Cluster (WSFC) configuration into the DR site. Reasons include the following possibilities:
- The infrastructure or staff can't maintain the WSFC configurations between different sites.
- You can’t leverage the target server in the DR site in the WSFC configuration because it is already part of another WSFC configuration.
- The service level agreements (SLAs) on recovery point objective (RPO) and recovery time objective (RTO) force a fast recovery from manual error, which can be realized only with a delayed recovery restoring the transaction log backups on one instance of the high availability (HA) and DR strategy.
Therefore, you need to supply the target server, which is in the DR site, by using log shipping to ship the transaction log from backups performed in the main site on the current primary.
Prerequisites for using log shipping
Before you set up log shipping, make sure you meet the following prerequisites:
- The primary database must use the full or bulk-logged recovery model. Switching the database to simple recovery causes log shipping to stop functioning.
- Before you configure log shipping, you must create a shared path to make the transaction log backups available to the secondary server.
- The log-shipping stored procedures require membership in the sysadmin fixed server role.
- The backup shared path should have read and write permissions to the SQL Server service account.
Configure log shipping DR solution example
In this example, we have already setup AlwasyOn between the primary replica server, called PRIMEHEAD, and your secondary replica, called HEAD2, as shown in the following image:
This section provides a step-by-step solution to configure log shipping on a database that is already a part of an AlwaysOn AG.
Configure log shipping for the AdventureWork2014 database between the PRIMEHEAD and the DR server, HEAD3.
While configuring log shipping on the database, take a full backup of the
AdventureWork2014 database and restore it on HEAD3 with non-recovery.
You need to create a shared folder on PRIMEHEAD to store the log backup that
LSCopy (log shipping) job uses.
Right-click on the database, select Properties, and click on the Transaction Log Shipping option on the left side of PRIMEHEAD. Then, click on the highlighted Enable this as a primary database in a log shipping configuration checkbox as shown in the following image:
Click Backup Setting to configure the LS Backup option. Select the network-shared path for LS Backup, as shown in the following image:
At this point, you can also schedule LS Backup according to your requirements. However, in this scenario, use the default settings.
To add a DR server, click Add as shown in the following image:
Click Connect to connect to HEAD3, the DR server, as shown in the following image:
On the Initialize Secondary Database tab, select the third option because the database has already been initialized on HEAD3.
Click the Copy Files tab. In the Destination folder for copied files box, type the path where transaction log backups are copied. For this scenario, use C:\LSCopyAlwaysOn for the path, as shown in the following image:
On the Restore Transaction Log tab, under Database state when restoring backups, choose either No recovery mode or Standby mode, as shown in the following image:
In this example, we selected No recovery mode, which implies that the DR database is not accessible. If you select Standby Mode, the DR database is available to the end user in read-only mode.
Click OK to start the log shipping.
The following screen displays:
To check the log shipping status, right-click on the DR server, HEAD3, instances, and select Reports->Standard reports—>Transactional Log Shipping Status. If the following screen appears, log shipping is healthy and working as expected.
If an AG fail over between PRIMEHEAD and HEAD2 occurs, log shipping is interrupted until you configure it considering AG specifications.
Now you can configure log shipping from HEAD2 to HEAD3, which will not impact log shipping functionality even if there is a fail over in the future between the AG replicas. Log backup always happens on the same path or location, regardless of which replica is serving as the primary.
You need to initiate a fail over between the replicas. Before initiating the fail over, complete the following steps:
Execute an LS backup job on primary replica and disable the job.
Execute an LS copy and restore job on secondary replica and then disable it.
To do this, right-click on the AG and select the fail over option as shown in the following image:
You can also accomplish this by using the following T-SQL commands to manually trigger an AG fail over:
USE master; GO ALTER AVAILABILITY GROUP [AGName] FAILOVER GO
After the fail over completes, the following window displays:
After an AG fail over between PRIMEHEAD and HEAD2, the current primary instance is HEAD2.
Follow the same steps to configure log shipping from the current primary server or node, HEAD2, to the DR Server, HEAD3. While configuring log shipping, choose the same shared path that you used during LS configuration between PRIMEHEAD and HEAD3, \Avail2017\lsbackup.
After the log shipping between HEAD2, the current primary, and HEAD3 completes, an LS backup job is created on HEAD2, and another set of LS copy and LS restore jobs are created on HEAD3.
Once again, initiate a fail over between AG replicas. Before initiating the fail over, make sure to complete the following steps:
Execute LS backup job on primary (HEAD2) and disable the job.
Execute LS copy and restore job on secondary (HEAD3) and then disable it.
After the final fail over, the current primary is PRIMEHEAD, HEAD2 is the secondary replica, and HEAD3 is the DR server. Because LS backup jobs exist on both the servers (primary and secondary), you need to modify LS backup job on both the PRIMEHEAD and HEAD2 to ensure that it only takes the log backup from the current primary.
To do this, add the following code to the job step 1:
Declare @dbname as varchar(20) Set @dbname=’AdventureWorks2014’ If sys.fn_hadr_backup_is_preferred_replica (@dbname)<>1 begin RAISERROR (50005,-- Message id, 16, -- Severity, 1, --State, N’This is not the primary server backup is rolled back’); end
The following image illustrates this:
After making the preceding changes, notice that the LS backup job starts failing on secondary server but runs fine on the primary.
Because there are two sets of LS copy and restore jobs on HEAD3, the DR server, you must ensure that only one set of jobs run at a time. You need to keep the jobs enabled that got created while configuring log shipping between HEAD2 and HEAD3 and disable the other set of jobs.
The following image shows more details:
Now, you have successfully configured log shipping on a database that is an existing part of an AlwaysOn AG. No matter which server is working as a primary server, your log shipping will be in sync.
Note: We strongly recommended that you do not make any changes in production without testing. Before implementing this solution in your production environment, first implement this configuration in a test environment.
a) Make sure that the backup job is running successfully on the current primary replica. b) The backup path should be the same as the shared path. c) Copy and restore jobs, which were created during LS configuration from HEAD2 to HEAD3 should run properly on the DR server. d) Check the Transactional Log Shipping Status in the standard report section.
Configuring log shipping on a highly available database enables you to have a DR server set up in a different data center. This setup proves helpful in case of a disaster and keeps your business unaffected while requiring minimal manual effort even if the servers in another data center are impacted.
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