Last week, Tad Brockway published a blog that announced the general availability notice of Azure Shared disks and some other enhancements. I had the opportunity to see Tad at an event in 2019 and the Azure team that he works with continues to bring great enhancements to the storage services.
Tad highlighted these two use cases (quoted from the blog):
SQL Server Failover Cluster Instances (FCI), Scale-out File Servers (SoFS), SAP ASCS/SCS running on Windows Server 2008+ (and beyond).
Linux applications running on GFS2, OCFS2, or distributed applications leveraging IO fencing on Linux including Red Hat Enterprise Linux High Availability (HA), SUSE Linux Enterprise HA and Ubuntu HA.
This is interesting as Server 2008 is supported, so some critical clusters that have remained on-premises beyond the end of life can get new compliance in Azure. Additionally, a strong Linux support comes from the start here.
The shared disk announcement is the main capability that should be recognized. This solves a very significant practical barrier to some Azure migrations: Application availability. I have long thought that the business reasons to deploy failover clusters are diminishing, but not extinct. Chances are, the reason clusters are in place today is for it running a critical application for a business. This may have remained on-premises for reasons to keep a cluster in place which may have hindered other Azure deployments of related or connected systems.
Now with Azure Shared Disks, life gets interesting in putting clustered apps in Azure! This Microsoft Doc explains how to set up an Azure Shared Disk and I recommend giving it a read as there are some specific requirements and region considerations. One interesting point is early on in the document that SCSI persistent reservations are supported, which allow clusters to come into Azure seamlessly. I hope we don’t see application vendors needlessly saying this isn’t supported, as it has the same storage requirements provided in Azure as it would on-premises. The figure below (Image reproduced from the Microsoft Docs post) shows an over of Azure Shared Disks:
Azure Shared Disk is an ‘apply to use’ type of capability it seems as you have to fill out this form to allow the Azure subscription to use this capability.
I can also see a use case of an easy way to ‘retire’ a production application in Azure that has been replaced with a SaaS solution. Example, if an organization has an application cluster that has been migrated to a new SaaS product but the application needs to be retained for the history and potentially any inquiries later, the Azure cluster deployment could be a nice ‘happily ever after’ locale for it.