Since the initial release of the Virtual Machine (VM) hosting service within Microsoft Azure there’s been a limitation on achieving the minimum requirements for the 99.9% SLA guarantee. This limitation has been that you needed to provision at least 2 VMs to get the SLA guarantee. That is until now. Now, there is an option to provision a single instance VM and have the 99.9% SLA guarantee too!
Microsoft is constantly working to improve and add new features / services to the Microsoft Azure platform. Among the latest of these changes is to support a 99.9% SLA with SINGLE instance VMs. While this isn’t a replacement for multi-instance VM configurations, this offers enhanced reliability for workloads where a single VM instance works.
Single Instance VM SLA Requirement
There are a few requirements that need to be met in order to achieve the 99.9% SLA guarantee for a single instance VM. The storage used for the VM Operating System and Data disks must be using Premium Storage. Premium Storage offers a much higher level of availability and performance with 5,000 IOPS per disk, versus 500 IOPS per disk with Standard Storage. The way Premium storage offers this is by utilizing SSD storage drives within the data center that are located on the same server hardware where the VM is running. Premium storage also offers a much higher throughput rate per disk of 2 Gbps.
Single Instance VMs must use Premium Storage to obtain 99.9% SLA guarantee.
Benefits of Multi-Instance VM Configuration
While it may sound appealing to configure your workloads to use a single instance VM, after all you can now get the 99.9% SLA guarantee, it’s still more advantageous to configure your workloads to use a multi-instance VM configuration instead. Among these is a higher SLA guarantee for multi-instance VMs of 99.95%.
Multi-Instance VM workloads achieve a higher 99.95% SLA guarantee.
For the vast majority of workloads it’s best to use a configuration consisting of multiple VM instances for added availability, reliability, and scalability. The best way to achieve all three of these is to use the Microsoft Azure service that is VM Scale Sets.
For more information on the SLA guarantee for Virtual Machines within Microsoft Azure, you can read the official SLA for Virtual Machines details page.