Recently I received an comparison from Azure with competitors. In the comparison there was stated that by default Azure provides an SLA of 99.95%. However, this is not entirely correct. By default a single basic virtual machine has no SLA at all!
I hear you thinking, what??? let me explain what the options are. First we need to know a bit more of the setup in Azure. For this explanation I will use West & North Europe. These regions do have Availability zones, but this might not always be the case. In the picture below you can review the Azure regions with their options.
So lets zoom in a bit further. In the picture below we have our 2 regions (West & North Europe). Within Region 1 we have 3 separated buildings, creating 3 availability zones.
So lets move on the SLA rules.
- For all Virtual Machines that have two or more instances deployed across two or more Availability Zones in the same Azure region, we guarantee you will have Virtual Machine Connectivity to at least one instance at least 99.99% of the time.
- For all Virtual Machines that have two or more instances deployed in the same Availability Set, we guarantee you will have Virtual Machine Connectivity to at least one instance at least 99.95% of the time.
- For any Single Virtual Machine using premium storage for all Operating System Disks and Data Disks, we guarantee you will have Virtual Machine Connectivity of at least 99.9%.
- For all other Single Virtual Machines there is no SLA.
Basically it means that if you want an SLA, you will need to use a virtual machine with full Premium SSD Storage, or deploy 2 virtual machines that are behind a load balancer or use other redundancy techniques. Keep in mind that Azure will need to update the hosts at some point, that might require a reboot of your virtual machine. In the rare cases that this might happen, Azure will reboot virtual machines at different times when they are in 1 update domain, with a different number.
The following Virtual Machine Series do support Premium SSD storage:
The following Virtual Machine Series do NOT support Premium SSD storage, and will always require 2 machines to receive an SLA:
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