PCD Practice Question: Designing highly scalable, available, and reliable cloud-native applications
This PCD practice question tests your understanding of designing highly scalable, available, and reliable cloud-native applications. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
A company runs a stateful application on Compute Engine with local SSDs. They want high durability. Which approach should they use?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Use persistent disks instead of local SSDs for automatic replication
Local SSDs are ephemeral and data is lost when the VM is stopped or terminated. Persistent disks, by contrast, automatically replicate data within the same zone (or across zones if using regional persistent disks), providing high durability. Option D correctly identifies that switching to persistent disks is the appropriate approach for durability, as local SSDs lack built-in redundancy.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
Replicate data to another zone using synchronous replication
Why it's wrong here
Synchronous replication adds complexity and latency, and is not a built-in feature of local SSDs.
✗
Use a RAID 1 array across multiple local SSDs
Why it's wrong here
RAID 1 provides redundancy but does not protect against zone or instance failure; local SSDs are still ephemeral.
✗
Take regular snapshots of local SSDs
Why it's wrong here
Snapshots are point-in-time backups, but data between snapshots is lost if the instance fails.
✓
Use persistent disks instead of local SSDs for automatic replication
Why this is correct
Persistent disks are automatically replicated within the same zone and can be configured for regional replication, offering high durability.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the misconception that local SSDs can be made durable through RAID or snapshots, but the core trap is that local SSDs are inherently ephemeral and cannot be used for durable storage regardless of redundancy techniques.
Detailed technical explanation
How to think about this question
Persistent disks use a distributed storage backend that replicates data synchronously within the zone (or across zones for regional PDs) using Google's Colossus file system, ensuring durability of 99.999999% (11 nines) annually. Local SSDs are physically attached to the host machine and provide higher IOPS but no replication; data is lost on host maintenance or VM migration. For stateful applications requiring both high performance and durability, a common pattern is to use local SSDs for caching or temporary data and persistent disks for persistent storage.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
An e-commerce site experiences heavy traffic on Black Friday and near-zero traffic during off-peak weeks. Rather than provisioning permanent large VMs, the team uses auto-scaling groups that add capacity automatically under load and reduce it overnight. Questions like this test whether you understand elasticity, availability zones, and cloud compute scaling patterns.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Designing highly scalable, available, and reliable cloud-native applications — This question tests Designing highly scalable, available, and reliable cloud-native applications — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Use persistent disks instead of local SSDs for automatic replication — Local SSDs are ephemeral and data is lost when the VM is stopped or terminated. Persistent disks, by contrast, automatically replicate data within the same zone (or across zones if using regional persistent disks), providing high durability. Option D correctly identifies that switching to persistent disks is the appropriate approach for durability, as local SSDs lack built-in redundancy.
What should I do if I get this PCD question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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