SLA for Virtual Machines

Question

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.
How to understand this sentence. Does this statement require that at least 2 instances be deployed in each available region? And these 2 available regions must be located in the same region.

Answer 1

Hello, @林鹏 !

The VM SLA of 99.99% means that you need to deploy at least two instances of your Virtual Machines across at least two Availability Zones within an Azure region. For example, VM1 deployed in Availability Zone 1 and VM2 deployed in Availability Zone 3 in the West US 2 Azure region. I'll go into more detail below.

What does the 99.99% Virtual Machine SLA mean when it talks about Availability Zones and Azure regions?
When you check the SLA for Virtual Machines, you are likely to see something like this:

https://azure.microsoft.com/en-us/support/legal/sla/virtual-machines/v1_8/

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.

Availability Sets, Availability Zones, and Azure Regions are much easier to understand when looking at diagrams (included below).

• Availability Set: A small, relatively local group of redundancy and reliability that protects you from things like power loss to a server rack or updates that you might encounter in a single fault domain. You get a 99.95% SLA when you have an availability set with 2 or more VMs.
• Availability Zone: A physically separate location (like a datacenter) within an Azure Region that provides redundancy and reliability that protects you from a disaster like a flood that might impact the whole datacenter. You get a 99.99% SLA when you have 2 VMs in two separate Availability Zones within the same region.
• Azure region: Datacenters deployed in an area that are connected through a dedicated regional low-latency network (less than 2ms). Examples would be West US 2, East US, UK South, Brazil South, Japan East, and Central India.

This means that if you deployed 2 VMs, each in a different Availability Zone within the same region, you would get an SLA of 99.99% availability for at least 1 VM. For example, VM1 deployed in Availability Zone 1 and VM2 deployed in Availability Zone 3 in the West US 2 Azure region.

Availability Zones within an Azure region:

Azure regions are located all around the world:

Deploying a VM in 1 of 3 Availability Zones within the Azure region West US 2:

Additional Reading:

• Availability Sets
• Availability Zones (and Regions)
• Azure regions with availability zone support
• SLA for Virtual Machines
• Clarification on the availability set, zone and LRS, ZRS discs