Availability Sets & Zones
Choosing between fault domains, update domains and zones to hit a target SLA without over-engineering.
Readiness
0%
1h 30m baseline
Exam memorization points
- An availability set protects against host and rack failure inside one datacenter and gives a 99.95% SLA.
- Availability zones protect against a whole datacenter failure inside a region and give a 99.99% SLA.
- Fault domains are separate physical groupings; update domains are maintenance batches. The default availability set uses 2 fault domains and 5 update domains.
- A VM cannot be moved into an availability set after deployment - the set must be chosen at creation time.
- A proximity placement group keeps VMs physically close for low latency, at the cost of reduced resilience options.
- Availability zones are a regional feature: not every region has zones, and zonal versus zone-redundant choices differ per service.
Traps & distractors
- Trying to add an existing VM to an availability set. It is only possible at creation (moving requires a redeploy or an ARM template change).
- Mixing availability sets with zones for the same tier of VMs - the patterns are alternatives, not layers.
- Assuming a single VM gets a 99.9% SLA regardless of disk type. Standard HDD or Standard SSD on a single VM does not reach it.
- Using a proximity placement group for a workload that needs zone resilience.
Suggested lab
Compare availability options
Build one availability set and one zone-spread pair and compare the reported SLA.
- 1Create an availability set with 2 fault domains and 5 update domains and place two VMs in it.
- 2Create two VMs placed in zone 1 and zone 2 with a Standard public IP.
- 3Inspect where each VM landed (fault domain, update domain, zone) on the VM overview blade.
- 4Attempt to move the availability-set VM into zone 1 and confirm the operation is not available.
- 5Record the SLA you expect from each pattern and compare with the availability blade.
Microsoft Learn
- Availability options for Azure virtual machinesdoc
- Search Microsoft Learn: availability zone fault domain update domain SLA virtual machinesearch
Live Microsoft Learn ingestion is a Sprint 2 item; until then links are curated and the search fallback always resolves.
Status
No time invested yet. Baseline assumptions only.
Self-assessed mastery
0%
High priority
Strong exam value. Schedule this week.
- Exam importance60% × 30% = 18.0
Learner-agnostic frequency on the real exam (3/5).
- Blueprint weight100% × 25% = 25.0
This topic's domain carries 22.5% of the exam objectives.
- Dependency leverage0% × 20% = 0.0
Nothing else in the graph depends on this topic.
- Current gap100% × 25% = 25.0
Readiness is 0%, so 100% of the topic is still uncovered.
Exam Priority Score = 30% importance + 25% blueprint + 20% dependency + 25% gap. Importance is exam frequency, blueprint is the domain's official exam weight, dependency is how many later topics this one unlocks, and gap is how far you currently are from ready.
Unlocks next
Leaf topic - nothing depends on it.
Baseline study time
1h 30m
Complexity
3 / 5
Remaining to target
1h 17m
Status weight
0%
Topics: availability set, availability zone, fault domain, update domain, sla, proximity
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