SQL Server Always On Availability Groups are an enterprise-level high-availability and disaster-recovery feature introduced the first time in SQL Server 2012as an alternative to database mirroring. A set of user databases that fail over together forms the availability group. These availability databases are hosted by the availability replicas and can be readable- writable at the primary replica and up to eight sets of secondary replica databases that can be configured to be read-only databases. The availability groups fail over due to the availability replica’s level issues and not the ones caused due to database level issues such as data loss or database corruption.Read more »
With all of the high-availability (HA) and disaster recovery (DR) features, the database administrator must understand how much data loss and downtime is possible under the worst case scenarios. Data loss affects your ability to meet recovery point objectives (RPO) and downtime affects your recovery time objectives (RTO). When using Availability Groups (AGs), your RTO and RPO rely upon the replication of transaction log records between at least two replicas to be extremely fast. The worse the performance, the more potential data loss will occur and the longer it can take for a failed over database to come back online.Read more »
This article is a continuation of a guide where we are checking all the available backup preferences for a database contained in an Availability Group.Read more »
Since the AlwaysOn Availabiliy Groups feature was introduced, we got new options to make the backups strategy more complete, but also more complex. Taking an advantage of secondary replicas, we can offload both, the FULL and even the Transaction Log backups from the Primary Replica to the Secondary, leaving the Primary replica dedicated to serve the production application.Read more »
Here we are with the last part of this series of articles! In this article we are going to see two curiosities:
- How does in-memory OLTP work with Availability Group?
- Can I migrate from Log Shipping or Database Mirroring to Availability Groups?
So, let’s start!Read more »
In continuation to the Availability Groups series, here you have another curiosity coming to make your job easier and help you to provide a solution to your customers 🙂
This time we will be talking about listeners. Basically, we will be talking about the limitation of one listener per Availability Group. If you never tested / tried this, this is what happens when you already have a listener in the Availability Group, and try to create another one:Read more »
We all love Availability Groups! Since its introduction in the SQL Server 2012, some things changed. In the beginning it was seen as “just a replacement for the database mirroring”, but when we discovered that this would support readable secondary’s, the possibility of having a listener and get rid of the shared storage – even being based on a Failover Cluster – we saw that Availability Groups is a special feature. Read more »
We have already configured our Availability Group, now we need to make it flexible and accessible. It’s time to check on how to create a listener in order to make a single access point for you AG!
In continuation to our previous article, we are going to pass to another phase of this setup, as we already have our database in sync and safe, or highly available, depending of the chosen mode/architecture.Read more »
In this article we are going to explore how to configure an Availability Group between a clustered instance and a standalone instance, showing, step-by-step, how to setup a possible Disaster Recovery environment.
Introduced on SQL Server 2012, the Availability Groups brought the expectation to be an improved version of the database mirroring, which will be discontinued soon. The AlwaysOn Availability Groups was improved on SQL Server 2014, giving the capability of have more replicas, better troubleshooting possibilities and improving its availability. Comparing the Availability Groups with the database mirroring, in a very high level, we gained the possibility of have a listener to dynamically redirect the connection to the current active instance and also the capability of distribute the read workload between readable replicas. However, only the primary replica is able to write.Read more »