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Category: HA / DR

High Availability Changes in SQL Server 2016

Martin Surasky looks at what SQL Server 2016 changed with respect to High Availability options:

AlwaysOn Availability Groups, first introduced in SQL Server 2012 is a feature that is conceptually similar to database mirroring. I’m going to assume you already know what AlwaysOn Availability Groups are in general, their main purpose and how they are different (essential aspects at least) from other technologies to provide replication such as Database Mirroring.

In SQL Server 2014, the significant enhancement to availability groups was the increase in the number of supported secondary replicas from three to eight. SQL Server 2016 includes a number of new enhancements

The biggest thing about it, as I recall, was stability: I wouldn’t have recommended too many places go into production with Availability Groups in 2012, but by 2016, many of the biggest bugs were ironed out.

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Creating a Failover Cluster Instance with Shared Storage

Ryan Adams wraps up a video series on setting up a SQL Server lab environment:

You are going to create a SQL Server Failover Cluster Instance in Part 4 of our series on how to build a SQL Cluster Lab. The FCI will only be installed on Node1 and Node2. FCIs require shared storage so you will make your domain controller an iSCSI target. Last you will create your FCI using the iSCSI drives you presented to the cluster. 

Click through for links to the entire series.

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High Availability Announcements from Microsoft

Allan Hirt looks at a couple announcements from Microsoft:

I’m going to discuss what I feel are the biggest game changers. I knew licensing was changing as I had conversations with Microsoft around this months ago. I was not sure what the final result was going to be, but I’m fairly pleased. Is it perfect? No, but it’s much better than it was.

You’ll definitely want to read Allan’s thoughts on Microsoft’s SQL Server licensing changes, as well as a private preview of Azure Shared Disks.

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MultiSubNetFailover and Availablity Groups

William Assaf strongly advises setting MultiSubNetFailover=True in connection strings when using Availability Groups:

I received an email from a client who is having issues with third-party applications connecting to their three-subnet SQL Server Availability Group. After an exchange with Microsoft Support, they discovered that the applications weren’t specifying MultiSubNetFailover = True in their connection strings. As a result, because RegisterAllProvidersIP = 1 in the cluster, connections were randomly experiencing high latency upon connecting, as client-side DNS queries over time had a 66% chance of returning the wrong IP from the listener.

They set RegisterAllProvidersIP = 0, but before you take that as advice keep reading.

Read on to learn why this is not a first-best solution.

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Building a SQL Cluster Lab

Ryan Adams has started a series on building a Windows cluster in Hyper-V and layering SQL Server on top of it:

Before we start to build a SQL Cluster Lab, let’s look at the desired result. You will build a 3-node cluster replicating an environment that has two data centers. As a result, the first two nodes will reside in data center 1 and the third node in data center 2. We are creating this architecture because it is the most common architecture I see for Availability Groups. It is multi-subnet and can solve for both HA and DR.

You will notice the domain controller in the middle. That piece is certainly not representative of a production environment. However, we are using it in our lab for several different functions and being a router is one of them.

Part 1 is the only part which is currently up, but this looks like it will be a good one. Go buy a couple more sticks of RAM for your PC and get reading.

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Accelerated Database Recovery

Andy Mallon explains the concept of Accelerated Database Recovery:

Accelerated Database Recovery(ADR) is a new feature intended to speed up the recovery process, which could be very slow, particularly when there are long-running, large transactions. ADR is not just for recovery after a crash, but also helps in other scenarios where the transaction log needs to be recovered–including Availability Group secondary redo and Failover Cluster Instance failovers.

This is one of the most interesting new features in SQL Server 2019.

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Disaster Recovery With Kafka Deployments

Yeva Byzek walks us through a disaster recovery scenario when running Apache Kafka:

Imagine:

Disaster strikes—catastrophic hardware failure, software failure, power outage, denial of service attack or some other event causes one datacenter with an Apache Kafka® cluster to completely fail. Yet Kafka continues running in another datacenter, and it already has a copy of the data from the original datacenter, replicated to and from the same topic names. Client applications switch from the failed cluster to the running cluster and automatically resume data consumption in the new datacenter based on where it left off in the original datacenter. The business has minimized downtime and data loss resulting from the disaster, and continues to run its mission critical applications.

Ultimately, enabling the business to continue running is what disaster recovery planning is all about, as datacenter downtime and data loss can result in businesses losing revenue or entirely halting operations. To minimize the downtime and data loss resulting from a disaster, enterprises should create business continuity plans and disaster recovery strategies.

Distributed data sources can still succumb to disaster and many of the same policies that people learn when working with relational databases apply to things like Kafka as well.

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Testing Azure SQL Database Failover

Arun Sirpal shows us how easy it is to fail over Azure SQL Database to another region:

So what happens now if I connect to the read/write endpoint? (I test this via SSMS)

The dreaded IP address / create a new firewall rule message. Why? Well this setup utilized a “server” level firewall rule and the server in the US did NOT have the IP address mapped in, you can see from the below screen shot that there are no firewall rules configured.

Fixing this is easy, you could just add the IP address on the secondary server as another server level rule but you should seriously consider using a database level firewall rule, the setup will get replicated to the secondary server making failover experience smoother.

Read on to see how to set this.

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Simplified Disaster Recovery With dbatools

Chrissy LeMaire shows how you can make DR a lot easier with dbatools:

When we talk about Disaster Recovery or DR, it’s often coupled with the term High Availability or HA. Here are some definitions from my graduate course on HADR.

high availability

  • Deals with minor outages, and failover solutions are automated
  • The goal is to restore full system functionality in a short time

disaster recovery

  • Deals with major outages such as natural and man-made disasters
  • Focuses on manual processes and procedures to restore systems back to their original state
  • Characterized by a phased approach to restoring the primary site

In the context of SQL Server, HA would be Availability Groups (AG), Failover Clustering (FCI), Log Shipping and more. I won’t be addressing High Availability in this post, however.

Chrissy has a demo of everything in action, including running a series of tests to ensure that your DR site actually has everything.

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HA/DR With Azure SQL Database

James Serra explains the High Availability and Disaster Recovery options available when using Azure SQL Database:

High Availability (HA) – Keeping your database up 100% of the time with no data loss during common problems.  Redundancy at system level, focus on failover, addresses single predictable failure, focus is on technology.  SQL Server IaaS would handle this with:

  • Always On Failover cluster instances
  • Always On Availability Groups (in same Azure region)
  • SQL Server data files in Azure

Disaster Recovery (DR) – Protection if major disaster or unusual failure wipes out your database.  Use of alternate site, focus on re-establishing services, addresses multiple failures, includes people and processes to execute recovery.  Usually includes HA also.  SQL Server IaaS would handle this with:

  • Log Shipping

  • Database Mirroring

  • Always On Availability Groups (different Azure regions)

  • Backup to Azure

Click through for more details.

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