Behavior of single VM with no infrastructure redundancy but with ZRS Disks at a zone outage

Question

Hello,

how behave a VM with no infrastructure redundancy but with attached ZRS Disks (OS+Data) at a zone outage?
Does it run without an issue if the compute resources are located in a different zone?
If not, does the allocator manage to self restart the VM in another zone with a healthy phyisical host?

thank you

Answer 1

Hello @Mares Martin ,

Thank you for reaching out to the Microsoft Q&A platform. Happy to answer your question. Please find answers in-line to your specific questions.

**VM with no infrastructure redundancy but with attached ZRS Disks (OS+Data) at a zone outage? **
As you know "Availability Zones" for VM redundancy is different from "Zone-redundant storage for managed disks". A ZRS disk lets you recover from failures in availability zones. If a zone went down, a ZRS disk can be attached to a virtual machine (VM) in a different zone. ZRS disks can also be shared between VMs for improved availability with clustered or distributed applications like SQL FCI, SAP ASCS/SCS, or GFS2. A shared ZRS disk can be attached to primary and secondary VMs in different zones to take advantage of both ZRS and availability zones.

Does it run without an issue if the compute resources are located in a different zone?
You can achieve high availability for your workloads using application-level replication across two zones, for example, SQL Always On. However, suppose you are using industry-specific proprietary software or legacy applications like older versions of SQL Server, which don't support application-level synchronous replication; ZRS disks will provide improved availability via storage-level replication. For example, if a zone goes down due to natural disasters or hardware failures, ZRS disk will continue to be operational. If your virtual machine (VM) in the affected Zone becomes unavailable, you could use a virtual machine in another zone and attach the same ZRS disk.

I highly recommend watching this video for detailed understanding of ZRS option for high availability with azure disks: https://www.youtube.com/watch?v=RSHmhmdHXcY

If not, does the allocator manage to self restart the VM in another zone with a healthy physical host?
No, If your virtual machine (VM) in the affected Zone becomes unavailable, you could use a virtual machine in another zone and attach the same ZRS disk.

Please "Accept as Answer" and Upvote if the answer provided is useful, so that you can help others in the community looking for remediation for similar issues.

Answer 2

Hello @Prrudram-MSFT ,

If not, does the allocator manage to self restart the VM in another zone with a healthy physical host?
No, If your virtual machine (VM) in the affected Zone becomes unavailable, you could use a virtual machine in another zone and attach the same ZRS disk.

But if the VM or compute resource is not tagged to a Zone, is the VM switching to another zone internally in case of an issue?

thank you