How many VMs will be unavailable at once. Will they unavailable in sequence or parallelly. If parallel, how many from any subscription

Hi Amul Kumar,

Welcome to the Microsoft Q&A Platform! Thank you for asking your question here.

Azure maintenance is usually conducted in a rolling manner, where VMs in an availability set or VM scale set (VMSS) are updated one domain at a time. This approach minimizes downtime and ensures that not all VMs are affected simultaneously, maintaining application availability during updates. By updating each domain individually, Azure can effectively manage the impact on services, allowing for a smoother transition and reducing the risk of disruptions. When parallel maintenance is necessary, Azure typically limits the number of impacted VMs to minimize downtime across any given subscription or VM scale set. While Azure does not provide a specific limit on the maximum number of VMs that can be impacted simultaneously within a single subscription, they typically restrict the scale of concurrent maintenance to prevent significant downtime for a large number of VMs.

You can review specific maintenance details and schedules through the Azure Service Health dashboard in the portal, which provides real-time information on the scope and timing of planned maintenance events for your resources. You can also configure Service Health alerts to receive specific notifications for upcoming maintenance events that may impact your VMs.

For more information, please visit https://zcusa.951200.xyz/en-us/azure/virtual-machines/maintenance-and-updates https://zcusa.951200.xyz/en-us/azure/virtual-machines/maintenance-configurations

Please let us know if you have any further queries. I’m happy to assist you further.

Thank you.