Fault domain

When a virtual machine is provisioned and assigned to an availability set, it is assigned a fault domain. With Azure Resource Manager (ARM), each availability set has two or three fault domains by default depending on Azure regions. Some provide two, while others provide three fault domains in an availability set. Fault domains are non-configurable by users. When multiple virtual machines are created, they are placed on separate fault domains. If more than five virtual machines are provisioned on an availability set, they are placed in a round-robin fashion on five fault domains. Fault domains are related to physical racks in the Azure data center. Fault domains provide High Availability from unplanned maintenance due to hardware, power, and network failure. Since a single virtual machine is only placed on a rack, other virtual machines continue running in case the rack in consideration snaps off.