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After a user creates an Availaiblity set, they can select it when they are create a VM, as for private cloud layers.
The user Before they deploy the VM, to change the Availability set before they deploy the VM by editing , the user can edit the VM.
If the user does not deploy the VM before the VDC is synchronized, the platform will remove the VM from the Availability set during the synchronization process.
During an upgrade, the platform will detect availability sets that contain deployed VMs. To detect other availability sets, the user should synchronize the virtual datacenter or networks.
For more information about Availability sets, see https://docs.microsoft.com/en-us/azure/virtual-machines/windows/tutorial-availability-sets.