For many years one of the challenges we had with customers, is that Azure didn’t have an SLA for single instance VMs. The recommendation is always to have two VM instances added to an availability set, which will make sure that the customer are covered under Microsoft SLA for VM Update time which is 99.95%.
A recent announcement from Microsoft states that they now support for Single Instance VM within Azure with an SLA of 99.9% provided that the VMs are running on Premium Storage. Which means that the VMs needs to be created using DS / GS or F_S series VMs and the storage account needs to be created using Premium Storage for hosting these VMs.
More information, please refer link below