AZ-900 Practice Question 84: Availability Set Cannot Span Zones
Microsoft Azure Fundamentals (AZ-900) · Test 9 · question 4 of 10
Six VMs run a critical workload in a region that supports three availability zones. To maximize resiliency, an engineer proposes putting all six VMs into one availability set and then configuring that set to span all three zones, so the VMs get fault-domain isolation and zone-level isolation at the same time. What should the team do instead?
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Answer:
Availability sets and availability zones solve the same problem at two different scopes, and they don't stack. An availability set spreads VMs across fault and update domains inside a single datacenter; Microsoft's own guidance is that once a region offers zones, "for more reliability than availability sets offer, use availability zones," and that sets are "especially useful in regions that don't support availability zones." An availability set has no property for pinning itself across multiple zones (only VMs (and VM Scale Sets) carry a zones setting), so the correct move for zone-level resiliency is to deploy the VMs straight into zones 1, 2, and 3, not to wrap them in a set.
Option A describes a capability that doesn't exist: an availability set cannot be assigned to more than one zone, so "proceeding as proposed" isn't possible. Option C, zone-redundant storage, protects the replicas of *stored data* across zones; it says nothing about where the *compute* runs, so the VMs' placement problem is untouched. Option D is not a valid configuration either; a single VM belongs to exactly one availability set, and even three separate sets would each still be confined to one datacenter, never spanning zones.
Reference: Availability sets overview