SQL Server Failover Cluster Instance

About Using Amazon FSX for SQL Server Failover Cluster Instance

February 14, 2021 by Jason Aw Leave a Comment

Using Amazon FSX for SQL Server Failover Cluster Instance – What You Need To Know!

If you are considering deploying your own Microsoft SQL Server instances in AWS EC2, you have some decisions to make regarding the resiliency of the solution. Sure, AWS will offer you a 99.99% SLA on your Compute resources if you deploy two or more instances across different availability zones. But don’t be fooled, there are a lot of other factors you need to consider when calculating your true application availability. I recently blogged about how to calculate your application availability in the cloud. You probably should have a quick read of that article before you move on.

When it comes to ensuring your Microsoft SQL Server instance is highly available, it really comes down to two basic choices: Always On Availability Group (AG) or SQL Server Failover Cluster Instance (FCI). If you are reading this article I’m making an assumption you are well aware of both of these options and are seriously considering using a SQL Server Failover Cluster Instance instead of a SQL Server Always On AG.

Benefits Of A Microsoft SQL Server Failover Cluster Instance

The following list summarize what AWS says are the benefits of a SQL Server FCI:

FCI is generally preferable over AG for SQL Server high availability deployments when the following are priority concerns for your use case:

License cost efficiency: You need the Enterprise Edition license of SQL Server to run AGs, whereas you only need the Standard Edition license to run FCIs. This is typically 50–60% less expensive than the Enterprise Edition. Although you can run a Basic version of AGs on Standard Edition starting from SQL Server 2016, it carries the limitation of supporting only one database per AG. This can become a challenge when dealing with applications that require multiple databases like SharePoint.

Instance-level protection versus database-level protection: With FCI, the entire instance is protected – if the primary node becomes unavailable, the entire instance is moved to the standby node. This takes care of the SQL Server logins, SQL Server Agent jobs, certificates, etc. that are stored in the system databases, which are physically stored in shared storage. With AG, on the other hand, only the databases in the group are protected, and system databases cannot be added to an AG – only user databases are allowed. It is the database administrator’s responsibility to replicate changes to system objects on all AG replicas. This leaves the possibility of human error causing the database to become inaccessible to the application.

DTC feature support: If you’re using SQL Server 2012 or 2014, and your application uses Distributed Transaction Coordinator (DTC), you are not able to use an AG as it is not supported. Use FCI in this situation.

https://aws.amazon.com/blogs/storage/simplify-your-microsoft-sql-server-high-availability-deployments-using-amazon-fsx-for-windows-file-server/

Challenges With FCI In The Cloud

Of course. The challenge with building an FCI that spans availability zones is the lack of a shared storage device that is normally required. Because the nodes of the cluster are distributed across multiple datacenters, a traditional SAN is not a viable option for shared storage. That leaves us with a two choices for cluster storage: 3rd party storage class resources like SIOS DataKeeper or the new Amazon FSx.

Let’s take a look at what you need to know before you make your choice.

SERVICE LEVEL AGREEMENT

As I wrote in how to calculate your application availability, your overall application SLA is only as good as your weakest link. In this case, the FSx SLA of 99.9%.

Normally 99.99% availability represents the starting point of what is considered “highly available”. This is what AWS promises you for your compute resources when two or more are deployed in different availability zones.

In case you didn’t know the difference between three nines and four nines…

99.9% availability allows for 43.83 minutes of downtime per month
99.99% availability allows for only 4.38 minutes of downtime per month

By hosting your cluster storage on FSx despite your 99.99% compute availability, your overall application availability will be 99.9%. In contrast, EBS volumes that span availability zones, such as in a DataKeeper deployment, qualifies for the 99.99% SLA at both the storage and compute layers. This means your overall application availability is 99.99%.

STORAGE LOCATION

When configuring FSx for high availability, you will want to enable multi-AZ support. By enabling multi-AZ you have an effectively have a “preferred” AZ and a “standby” AZ. When you deploy your SQL Server FCI nodes you will want to distribute those nodes across the same AZs.

Now in normal situations, you will want to make sure the active cluster node resides in the same AZ as the preferred FSx storage node. This is to minimize the distance and latency to your storage. But also to minimize the costs associated with data transfer across AZs. As specified in the FSx price guide, “Standard data transfer fees apply for inter-AZ or inter-region access to file systems.”

In the unfortunate circumstance where you have a SQL Server FCI failure, but not a FSx failure, there is no mechanism to tie both the storage and compute together. In the event that FSx fails over, it will automatically fail back to the primary availability zone. However, best practices dictate SQL FCI remain running on the secondary node until root cause analysis is performed and fail back is typically scheduled to occur during maintenance periods. This leaves you in a situation where your storage resides in a different AZ, which will incur additional costs. Currently the cost for transferring data across AZs, both ingress and egress, is $0.01/GB.

Without keeping a close eye on the state of your FSx and SQL Server FCI, you may not even be aware that they are running in different regions until you see the data transfer charge at the end of the month.

In contrast, in a configuration that use SIOS DataKeeper, the storage failover is part of the SQL Server FCI recovery, ensuring that the storage always fails over with the SQL Server instance. This ensures SQL Server is always reading and writing to the EBS volumes that are directly attached to the active node. Keep in mind, DataKeeper will incur a data transfer cost associated with write operations which are replicated between AZs or regions. This data transfer cost can be minimized with the use of compression available in DataKeeper.

CONTROLLING FAILOVER

In an FSx multi-subnet configuration, there is a preferred availability zone and a standby availability. Should the FSx file server in the preferred availability zone experience a failure, the file server in the standby AZ will recover. AWS reports that this recovery time takes about 30 seconds with standard shares. With the use of continuously available file shares, Microsoft reports this failover time can be closer to 15 seconds. During this failover time, there is a brownout that occurs where reads and writes are paused, but will continue once recovery completes.

FSx multi-site has automatic failback enabled. This means that for every unplanned failover of FSx, you also have an unplanned failback. In contrast, typically when a SQL Server FCI experience an unplanned failover you would either just leave it running on the secondary or schedule a failback after hours or during the next maintenance period.

SQL SERVER ANALYSIS SERVICES CLUSTER NOT SUPPORTED WITH FSX

If you want to cluster SSAS, you will need a clustered disk resource like SIOS DataKeeper. The How to Cluster SQL Server Analysis Server white paper clearly states that SMB cannot be used and that cluster drives with drive letters must be used. In contrast, the DataKeeper Volume resource presents itself as a clustered disk and can be used with SSAS.

Summary

While FSx certainly can make sense for typical SMB uses like Windows user files and other non-critical services where 99.9% availability SLA suffices, FSx is an excellent option If you application requires high availability (99.99%) or HA/DR solutions that also span regions, the SIOS DataKeeper is the right fit.

Reproduced with permission from Clusteringformeremortals

Configure SQL Server Failover Cluster Instance On Azure Virtual Machines

April 4, 2019 by Jason Aw Leave a Comment

Configure SQL Server Failover Cluster Instance On Azure Virtual Machines With Msdtc #Sql #Azure #Msdtc

You probably know that we have included plenty of step-by-step guides for building SQL Server Failover Cluster Instances (FCI) on Azure, from SQL Server 2008 through the latest. Here are some links to get you started. But really there is very little difference in the configuration between the different versions of Windows and SQL Server. So I think you will be able to figure it out regardless of what versions you use.

STEP-BY-STEP: HOW TO CONFIGURE A SQL SERVER FAILOVER CLUSTER INSTANCE (FCI) IN MICROSOFT AZURE IAAS #SQLSERVER #AZURE #SANLESS

STEP-BY-STEP: HOW TO CONFIGURE A SQL SERVER 2008 R2 FAILOVER CLUSTER INSTANCE IN AZURE

What I have not addressed is what to do about MSDTC. Microsoft addressed that in this article posted here.

https://blogs.msdn.microsoft.com/sql_pfe_blog/2018/07/05/configure-sql-server-failover-cluster-instance-on-azure-virtual-machines-with-msdtc

However, that article/video only addresses SQL Server 2016 and later. The good news is that most of that guidance can be applied to SQL Server 2008/2012/2014. Until I have time to do a proper step-by-step guide I wanted to jot down some basic notes, more as a reminder to myself. However, you might find this information useful as well in the meantime.

The steps below assume you have already created a SQL Server FCI in Azure and clustered the DTC resource. Reference the guides above for the details on those steps. The steps below really just detail the load balancer configuration required in Azure to make this work.

Create Load Balancer For MSDTC

The MSDTC resource will require its own load balancer. Instead of creating a new load balancer, we will add a new frontend to the load balancer that should already be configured for the SQL Server FCI. Of course this frontend IP address should match the cluster IP address associated with the clustered MSDTC resource.

For the backend pool just reuse the existing pool that you created that contains the SQL cluster nodes.

You will need to create a new health probe dedicated to the MSDTC resource. The port you use has to be different than the one you used for the SQL resource. Don’t use 59999. Maybe use something like 49999.

The final step is to create the load balancing rule for MSDTC. Create a new rule and reference the MSDTC frontend that we just created and the existing backend. Next we need to create a new load balancing rule. MSDTC uses ephemeral ports, which is a big range of ports. As you create the rule, you have to select the box that says “HA Ports”. Finally, make sure Direct Server Return is enabled.

Update MSDTC Cluster IP Resource

Works like the SQL Server Cluster IP address. We need to run a Powershell command that will for the MSDTC cluster IP resource to respond to the health probe we just created that probes port 49999. It also sets the subnet mask of that MSDTC cluster IP address to 255.255.255.255 to avoid IP address conflicts with the load balancer frontend we setup that shares the same address.

# Define variables $ClusterNetworkName = “”  
# the cluster network name (Use Get-ClusterNetwork on 
Windows Server 2012 of higher to find the name of the MSDTC resource) 
$IPResourceName = “”  
# the IP Address resource name of the MSDTC resource  $ILBIP = “”  
# the IP Address of the Internal Load Balancer (ILB) and MSDTC resource 
Import-Module FailoverClusters 
# If you are using Windows Server 2012 or higher: 
Get-ClusterResource $IPResourceName | Set-ClusterParameter 
-Multiple @{Address=$ILBIP;ProbePort=49999;SubnetMask="255.255.255.255";
Network=$ClusterNetworkName;EnableDhcp=0} 
# If you are using Windows Server 2008 R2 use this:  
#cluster res $IPResourceName /priv enabledhcp=0 address=$ILBIP probeport=59999  
subnetmask=255.255.255.255

Confirm It Is Working!

You can use DTCPing or go into Component Services and look under Computers>My Computers>Distributed Transaction Coordinator where you should see a local DTC and a clustered DTC. Any distributed transactions should appear in the clustered DTC, not the local DTC. Check out this video for an example of how to create a distributed transaction for testing.

Next Steps

This is a quick and dirty guide. For the experienced user it should get your MSDTC resource up and running in Azure. I’ll be publishing a detailed step-by-step guide in the near future. In the meantime, if you get stuck don’t hesitate to reach out to me on Twitter @daveberm

Achieving SQL Server High Availability Disaster Recovery With DataKeeper

March 26, 2019 by Jason Aw Leave a Comment

Achieve SQL Server High Availability, Disaster Recovery With A Mix Of Always On Availability Groups And SANless SQL Server Failover Cluster Instances

Introduction

The topic of mixing SQL Server Failover Cluster Instances (FCI) with Always On Availability Groups (AG) is pretty well documented. However, most of the available documentation documents configurations that assume the SQL Server FCI portion of the solution utilizes shared storage. What if I want to build a SANless SQL Server FCI using Storage Spaces Direct (S2D), can I still add a SQL Server AG to the mix? Unfortunately, the answer to this question is no. As of today, this combination of S2D based SQL Server FCI and Always On AG is not supported. I previously blogged about this S2D limitation here.

However, the good news is you CAN build a SANless SQL Server FCI with SIOS DataKeeper and still leverage Always On AG for things like readable secondaries. You still have to abide by the same rules that apply when mixing traditional SAN based SQL Server FCI and Always On AGs, but most part to achieve SQL Server high availability is about the same.

DataKeeper Synchronous replication is commonly used between nodes in the same data center or cloud region, but you may want to replicate asynchronously to an additional node in a different region for disaster recovery. In this case, if you ever do have to bring the DR node online after an unexpected failure, you will have to scrap the Always On AG configurations and reconfigure them. This requirement is very similar to to what Microsoft published here in regards to restoring asynchronous snapshots of SQL Server Always On AGs running inside VMs.

Availability Groups

Essentially, a SANLess SQL Server Failover Cluster Instance with DataKeeper looks like a single instance of SQL Server as far as the Always On Availability Group Wizard is concerned. The configuration of the Always On AG is exactly the same as if you were creating just an Always On AG between two Standalone (non-clustered) SQL Server instances.

The real confusion arise in the fact that in this configuration all the servers reside in the same failover cluster. But the SQL Server FCI is only configured to run only on the cluster nodes where SQL Server was installed as a Clustered SQL Server Instance. The other nodes are in the same cluster. However, SQL is installed on those nodes as a Standalone SQL Server Instance, not a Clustered Instance. It’s a bit confusing. Essentially what is happening is that Always On AG’s leverage the WSFC quorum model and listeners. As such all the AG Replicas need to reside in the same WSFC, even though they typically do not run clustered instances of SQL Server. If you are completely confused that is okay, most people are confused when they first try to wrap their head around this hybrid configuration.

The real benefit in a configuration like this is that a SQL Server Failover Cluster Instance can be a better and more cost effective (more on this later*) High Availability solution than Always On AG in many circumstances, but it lacks the ability to offer a readable secondary replica. Adding an Always On AG readable secondary replica becomes a viable option to address this need. And using SIOS DataKeeper eliminates the need for a SAN for the SQL Server FCI, which opens up the possibility of configuring SQL Server FCIs where nodes reside in different data center, which also means support for SQL Server FCI’s that span Availability Zones in both Azure and AWS.

Please note that pictured below is just one possible configuration. Multiple FCI cluster nodes, multiple AGs and multiple Replicas are all supported. You are only limited by the limits imposed by your version of SQL Server.

This article seems to document the setup steps pretty well. Of course, instead of shared storage for the SQL FCI, you will use SIOS DataKeeper to build the FCI as I document here.

Image result for SQL Server FCI with Availability Groups

Basic Availability Groups

As of SQL Server 2016 a scaled down “Basic Availability Groups” became available in SQL Server Standard Edition, making this configuration possible even in SQL Server Standard Edition. Basic AGs are limited to a single database per Availability Group, a Single Replica (2-nodes). However, they do not support a readable secondary replica so their use cases in this hybrid configuration are very limited.

Distributed Availability Groups

Distributed AGs were introduced in SQL Server 2016 are also supported in this hybrid configuration. Distributed AGs are very similar to regular AGs, but the Replicas do not need to reside in the same cluster, or even in the same Windows Domain. Microsoft documents the the main use cases of Distributed Availability Groups as follows:

Disaster recovery and easier multi-site configurations
Migration to new hardware or configurations, which might include using new hardware or changing the underlying operating systems
Increasing the number of readable replicas beyond eight in a single availability group by spanning multiple availability groups

Image result for distributed availability groups

Summary

If you like the idea of SQL Server FCIs for SQL Server high availability, but want the flexibility of read-only secondary replicas, this hybrid solution might just be the thing you are looking for. Traditional SAN based SQL Server FCIs, and even Storage Spaces Direct (S2D) based FCIs, limit you to a single data center. SIOS DataKeeper frees you from the limits of your SAN and enables configurations such as SQL Server FCI that span Availability Zones or Cloud Regions. It also eliminates the reliance on the SAN, allowing you to leverage locally attached high speed storage devices without giving up your SQL Server Failover Cluster Instance.

* How to Save Money

Earlier I promised I would tell you how to save money by doing this all with SQL Server Standard Edition. If you can live with readable replicas that are point in time based snapshots, you can skip Always On AGs completely and just use the SIOS DataKeeper target side snapshot feature to periodically take an application consistent snapshot of the volumes on the target server without impacting ongoing replication or availability. Here’s how…

http://discover.us.sios.com/rs/siostechnology/images/10-Ways-Save-AlwaysOn-vs-Failover-Clustering.pdf

Create a 2-node SQL Server FCI with SQL Server Standard Edition and save a boatload of money on SQL licenses. And yet still replicate the data to a 3rd node outside the cluster for reporting or DR purposes. If you take a snapshot of the volumes on this third server these snapshots are read-right accessible. This way, you can mount those databases from a standalone instance of SQL Server to run month end reports, copy to archives, or you might even want to use those snapshot to quickly and easily update your QA and Test/Dev environments with the latest SQL data.

I hope you found guide to create to achieve SQL Server high availability, disaster recovery with a mix of Always On Availability Groups and SANless SQL Server Failover Cluster Instances useful.

S2D For SQL Server Failover Cluster Instances

September 8, 2018 by Jason Aw Leave a Comment

Storage Spaces Direct For SQL Server Failover Cluster Instances

With the introduction of Windows Server 2016 Datacenter Edition a new feature called Storage Spaces Direct (S2D) was introduced. At a very high level, S2D For SQL Server Failover Cluster Instances allows you to pool together locally attached storage and present it to the cluster as a CSV for use in a Scale Out File Server. Then it can be accessed over SMB 3 and used to hold cluster data such as Hyper-V VMDK files. This can also be configured in a hyper-converged (HCI) fashion such that the application and data can all run on the same set of servers. This is a grossly over-simplified description, but for details, you will want to look here.

Image taken from https://docs.microsoft.com/en-us/windows-server/storage/storage-spaces/storage-spaces-direct-overview

The main use case targeted is hyper-converged infrastructure for Hyper-V deployments. However, there are other use cases, including leveraging this SMB storage to store SQL Server Data to be used in a SQL Server Failover Cluster Instance

Why would anyone want to do that?

Well, for starters you can now build a highly available 2-node SQL Server Failover Cluster Instance (FCI) with SQL Server Standard Edition, without the need for shared storage. Previously, if you wanted HA without a SAN you pretty much were driven to buy SQL Server Enterprise Edition and make use of Always On Availability Groups or purchase SIOS DataKeeper and leverage the 3rd party solution which lets you build SANless clusters with any version of Windows or SQL Server. SQL Server Enterprise Edition can really drive up the cost of your project, especially if you were only buying it for the Availability Groups feature.

In addition to the cost associated with Availability Groups, there are a number of other technical reasons why you might prefer a Failover Cluster over an AG. Application compatibility, instance vs. database level protection, large number of databases, DTC support, trained staff, etc., are just some of the technical reasons why you may want to stick with a Failover Cluster Instance.

SIOS DataKeeper Solution Vs S2D For SQL Server Failover Cluster Instances

Microsoft lists both the SIOS DataKeeper solution and the S2D solution as two of the supported solutions for SQL Server FCI in their documentation here.

https://docs.microsoft.com/en-us/azure/virtual-machines/windows/sql/virtual-machines-windows-sql-high-availability-dr

When comparing the two solutions, you have to take into account that SIOS has been allowing you to build SANless Clusters since 1999. But the S2D For SQL Server Failover Cluster Instances is still in its infancy. Having said that, there are bound to be some areas where S2D has some catching up to do. Or, simply features that they will never support simply due to the limitations with the technology.

Before Choosing Your SANless Cluster Solution

Have a look at the following table for an overview of some of the things you should consider before you choose your SANless cluster solution.

S2D For SQL Server Failover Cluster Instances

If we go through this chart, we see that SIOS DataKeeper clearly has some significant advantages. For one, DataKeeper supports a much wider range of platforms, going all the way back to Windows Server 2008 R2 and SQL Server 2008 R2. The S2D solution only supports the latest releases of Windows and SQL Server 2016/2017. S2D also requires the Datacenter Edition of Windows, which can add significantly to the cost of your deployment. In addition, SIOS delivers the ONLY HA/DR solution for SQL Server on Linux that works both on-prem and in the cloud.

Analysis Of The Differences

But beyond the cost and platform limitations, I think the most glaring gap comes when we start to consider disaster recovery options for your SANless cluster. Allan Hirt, SQL Server Cluster guru and fellow Microsoft Cloud and Datacenter Management MVP, recently posted about this S2D limitation. In his article Revisiting Storage Spaces Direct and SQL Server FCIs Allan points out that due to the lack of support for stretching S2D clusters across sites or including an S2D based cluster as a leg in an Always On Availability Group, the best option for DR in the S2D scenario is log shipping!

Don’t get me wrong. Log shipping has been around forever and will probably be around long after I’m gone. But that is taking a HUGE step backwards when we think about all the disaster recovery solutions we have become accustomed to, like multi-site clusters, Availability Groups, etc.

In contrast, the SIOS DataKeeper solution fully supports Always On Availability Groups. Better yet – it can allow you to stretch your FCI across sites to give you the best HA/DR solution you could hope to achieve in terms of RTO/RPO. In an Azure environment, DataKeeper also support Azure Site Recovery (ASR), giving you even more options for disaster recovery.

The rest of this chart is pretty self explanatory. It basically consist of a list hardware, storage and networking requirements that must be met before you can deploy an S2D cluster. An exhaustive list of S2D requirements is maintained here. https://docs.microsoft.com/en-us/windows-server/storage/storage-spaces/storage-spaces-direct-hardware-requirements

SIOS Datakeeper. What’s Good

The SIOS DataKeeper solution is much more lenient. It supports any locally attached storage and as long as the hardware passes cluster validation, it is a supported cluster configuration. The block level replication solution has been working great ever since 1 Gbps was considered a fast LAN and a T1 WAN connection was considered a luxury.

SANless clustering is particularly interesting for cloud deployments. The cloud does not offer traditional shared storage options for clusters. So for users in the middle of a “lift and shift” to the cloud that want to take their clusters with them they must look at alternate storage solutions. For cloud deployments, SIOS is certified for Azure, AWS and Google and available in the relevant cloud marketplace. While there doesn’t appear to be anything blocking deployment of S2D based clusters in Azure or Google, there is a conspicuous lack of documentation or supportability statements from Microsoft for those platforms.

Make A Safe Choice

SIOS DataKeeper has been doing this since 1999. SIOS has heard all the feature requests, uncovered all the bugs, and has a rock solid solution for SANless clusters that is time tested and proven. While Microsoft S2D is a promising technology, as a 1st generation product I would wait until the dust settles and some of the feature gap closes before I would consider it for my business critical applications.

To know more about S2D For SQL Server Failover Cluster Instances, find out here SIOS DataKeeper

Reproduced with permission from Clusteringformeremortals.com

Why Build A SQL server Failover Cluster Instance In Azure Cloud?

March 13, 2018 by Jason Aw Leave a Comment

Why Would You Want To Build A SQL server Failover Cluster Instance In The Azure Cloud?

There was an interesting discussion happening today in the Twitterverse. Basically, someone asked the question “Has anyone set up a SQL server Failover Cluster Instance in Azure?” The ensuing conversation involved some well respect SQL Server experts. And it led to the following question, “Why would you want to build a SQL Server AlwaysOn Failover Cluster instance in the cloud?”

That question could be interpreted in two ways: “Why do you need High Availability in the Cloud” or “Why wouldn’t you use AlwaysOn Availability Groups instead of Failover Cluster Instances?”

Let’s address each question one at a time.

Question 1 – Why do you need High Availability in the Azure Cloud?

You might think that just because you host your SQL Server instance in Azure, that you are covered by their 99.95% uptime SLA. If you think that, you would be wrong. In order to take advantage of the 99.95% SLA, you have to have at least two instances of SQL running in an Availability Set. With a single instance of SQL running, you can definitely expect that there will minimally be downtime during maintenance periods. But, you are also susceptible to unplanned failures.
Two instances of SQL Server cannot generally be load balanced. You have to implement some sort of mechanism to keep the servers in sync. To ensure that if there is a problem with one of the servers, the other server will be able to continue to service the requests. High Availability solutions like AlwaysOn Availability Groups, AlwaysOn Failover Cluster Instances and even the deprecated Database Mirroring can provide high availability for SQL Server in that scenario. Other solutions like log shipping and transactional replication may be able to help keep data synchronized between servers. But they are not typically considered high availability solutions and will not ensure the availability of your SQL Server.
Microsoft does occasionally need to perform maintenance on Azure that could bring down an entire Upgrade Domain and all the instances running in that Upgrade Domain. You don’t have any say on when this will happen. So, you need to have a mechanism in place to ensure that if they do have to bring down your primary SQL Server instance, you can expect that your secondary SQL Server instance will take over the workload without missing a beat. All of the high availability solutions mentioned above can ensure that you will continue to run in the event that Microsoft is doing maintenance on the Upgrade Domain of your primary server. Microsoft will only do maintenance on a single Upgrade Domain at a time. This ensures that your secondary server will still be online assuming you put the both in the same Availability Set.
What do you do if YOU want to performance maintenance on your production SQL Server? Maybe you want to install a Service Pack or other hotfix? Without a secondary server to fail over to, you will have to schedule planned downtime. One of the primary benefits of any high availability solution is the ability to do rolling upgrades, minimizing the impact of planned downtime.

Question 2 – Why wouldn’t you use AlwaysOn Availability Groups instead of Failover Cluster Instances?

Save Money! SQL Server AlwaysOn Availability Groups requires Enterprise Edition of SQL Server. Why not save money and deploy SQL Server Standard Edition and build a simple 2-node Failover Cluster Instance? Unless you need Enterprise Edition for some other reason, this is a no brainer.
Protect the ENTIRE SQL Server instance. AlwaysOn Availability Groups only protects user defined databases; you cannot protect the System and MSDB databases. If you build a SQL Server Failover Cluster Instance instead, you are protecting the ENTIRE instance, including the System and MSDB databases.
Ease Administration. In Azure, you are limited to just on client listener. This limits you to just one Availability Group. In contrast, with a Failover Cluster Instance one client listener is all you need, so there is no limitation.
Worker Thread Exhaustion. With AlwaysOn AG, you have to keep an eye on the available worker threads. The available worker threads limit the number of databases you can protect with AlwaysOn AG. In contrast, AlwaysOn Failover Clustering with DataKeeper block level replication does not consume more resources for each database you add. This means you can scale to protect hundreds of databases without the additional overhead associated with AlwaysOn AG.
Distribute Transaction Support. AlwaysOn AG does not support distributed transactions (DTC). If your application requires DTC support, you are going to have to look at an AlwaysOn Failover Cluster Instance instead.
Support of Other Replication Technologies. If you plan on setting up Peer to Peer replication between two databases protected by AlwaysOn AG you can forget about it. In fact, there are many restrictions you have to be aware of once you deploy AlwaysOn Availability Groups. AlwaysOn FCI’s do not have any of those restrictions.

Conclusion

Knowing what you know above, shouldn’t the question really be “Why would I want to implement AlwaysOn AG in the Cloud when I can have a much more robust and inexpensive solution building an AlwaysOn Failover Cluster instance?”

If you are interested in building an AlwaysOn Failover Cluster Instance in Azure, check out my blog post Step-by-Step: How to configure a SQL Server Failover Cluster Instance (FCI) in Microsoft Azure IaaS #SQLServer #Azure #SANLess

Reproduced with permission from https://clusteringformeremortals.com/2015/03/05/why-would-you-want-to-build-a-sqlserver-failover-cluster-instance-in-the-azure-cloud/