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3 min read

What’s new in failover clustering: #03 Stretched Clusters

This post was authored by Ned Pyle, Principal Program Manager, Windows Server

Why should you care about clustered storage? Everyone’s talking about apps, mobile, DevOps, containers, platforms. That’s cutting edge stuff in the IT world. Storage is boring, right?

Well, they’re all wrong. Storage is the key. You care about storage because it contains the only irreplaceable part of your IT environment: your data. That data is what makes your company run, what makes the money, what keeps the lights on. And that data usage is ever increasing.

Your datacenter could burn to the ground, all your servers could flood, your network could be shut down by a malicious attack, but if your data is safely protected, you can always get back to business.

Windows Server 2016 stretch clustering is here to protect that data and run those workloads so that your business stays in business.

Stretching clusters with Storage Replica in Windows Server 2016

Storage Replica offers new disaster recovery and preparedness capabilities to the already robust Failover Cluster in Windows Server 2016 Technical Preview. For the first time, Windows Server offers the peace of mind of a zero data loss recovery point objective, with the ability to synchronously protect data on different racks, floors, buildings, campuses, counties and cities. After a disaster strikes, all data will exist elsewhere, without any possibility of loss. The same applies before a disaster strikes; Storage Replica offers you the ability to switch workloads to safe locations prior to catastrophes when granted a few moments warning – again, with no data loss.

Storage Replica allows more efficient use of multiple datacenters. By stretching clusters or replicating clusters, workloads can be run in multiple datacenters for quicker data access by local proximity users and applications, as well as for better load distribution and use of compute resources. If a disaster takes one datacenter offline, you can move its typical workloads to the other site temporarily. It is also workload agnostic – you can replicate Hyper-V VMs, MS SQL Server databases, unstructured data or third party application workloads.

Stretch Cluster allows configuration of computers and storage in a single cluster, where some nodes share one set of asymmetric storage and some nodes share another, then synchronously or asynchronously replicate with site awareness. This scenario can utilize shared Storage Spaces on JBOD, SAN and iSCSI-attached LUNs. It is managed with PowerShell and the Failover Cluster Manager graphical tool, and allows for automated workload failover.

Synchronous Replication

Order of operation

Synchronous Replication




1. Application writes data
2. Log data is written
and the data is replicated to the remote site
3. Log data is written at the
remote site
4. Acknowledgement from the remote site
5. Application
write acknowledged


t & t1: Data flushed to the volume, logs always write through

Besides synchronous replication, Storage Replica can utilize asynchronous replication for higher latency networks or for lower bandwidth networks.

Ease of Deployment and Management

You deploy and manage stretch clusters using familiar and mature tools like Failover Cluster Manager, which means reduced training time for staff. Wizard-based setup allows administrators to quickly deploy new replication groups and protect their data and workloads.

To ensure successful deployment and operational guidance, Storage Replica and the Failover Cluster both provide validation mechanisms with detailed reports. For instance, prior to deploying a stretch cluster, you can test the topology for requirements, estimate sync times, log size recommendations and write IO performance.

Windows Server 2016 also implements site fault domains, allowing you to specify the location of nodes in your cluster and set preferences. For instance, you could specify New York and New Jersey sites, then ensure that all nodes in New York must be offline for the workloads and storage replication to automatically switch over to the New Jersey site. All of this is implemented through a simple PowerShell cmdlet, but can also be automated with XML files for larger private cloud environments.


Windows Server 2016 stretch clustering was designed with your data’s safety in mind. The mature, robust failover clustering combined with synchronous replication offer peace of mind at commodity pricing. Try this new feature in Windows Server 2016 and download the Technical Preview. For additional details, see the feature Cluster blog here.

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