The answer is to use a cluster with a mix of standard and preemptible VMs. This configuration minimizes cost because preemptible VMs cost roughly 80% less than standard instances, and mixing them with standard VMs provides essential fault tolerance for a 6-hour job. Since the job reads and writes directly to Cloud Storage rather than local HDFS, you avoid the risk of data loss if preemptible VMs are reclaimed, and you don’t need expensive local SSDs. On the Google Professional Data Engineer exam, this scenario tests your understanding of balancing cost and reliability in ephemeral workloads—a common trap is choosing a single-node cluster, which lacks the parallelism to process 500 TB within the time limit. The key insight is that preemptible VMs are ideal for stateless, fault-tolerant worker nodes, while standard VMs anchor the master and critical workers. Memory tip: “Preempt for price, standard for stability.”
PDE Practice Question: Building and operationalizing data processing systems
This PDE practice question tests your understanding of building and operationalizing data processing systems. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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 data engineer needs to process a large dataset (500 TB) stored in Cloud Storage using Dataproc. The processing job requires reading the entire dataset and writing results back to Cloud Storage. The job is expected to run for 6 hours. Which configuration minimizes cost?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Use a cluster with a mix of standard and preemptible VMs.
Option C is correct because preemptible VMs cost about 80% less than standard VMs, and mixing them with standard VMs provides fault tolerance for the job's 6-hour duration. Since the job reads and writes to Cloud Storage (not local HDFS), local SSDs are unnecessary, and a single-node cluster would lack the parallelism needed to process 500 TB efficiently within 6 hours. Using a mix of standard (for critical master/worker nodes) and preemptible VMs (for worker nodes) minimizes cost while ensuring job completion.
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.
✗
Use a single-node cluster with standard VMs.
Why it's wrong here
A single node may not have enough resources and is not cost-efficient for 500 TB.
✗
Use a cluster with local SSDs for faster I/O.
Why it's wrong here
Local SSDs are not necessary when reading from Cloud Storage.
✓
Use a cluster with a mix of standard and preemptible VMs.
Why this is correct
Preemptible VMs reduce cost significantly while providing sufficient compute.
Related concept
Read the scenario before looking for a memorised answer.
✗
Use a cluster with n1-highmem-32 instances and 1000 cores.
Why it's wrong here
High-memory instances are more expensive and may be overkill.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Google Cloud often tests the misconception that local SSDs always improve performance for data processing jobs, but in Dataproc, when data resides in Cloud Storage, the bottleneck is network throughput, not local disk speed, making SSDs an unnecessary cost.
Detailed technical explanation
How to think about this question
Preemptible VMs in Dataproc are Compute Engine instances that last up to 24 hours but can be terminated at any time; they are ideal for batch jobs that can tolerate interruptions, such as Spark jobs with checkpointing or resilient DAGs. Dataproc automatically handles preemption by relaunching tasks on standard VMs, so mixing instance types ensures job completion without manual intervention. The 6-hour runtime is well within the preemptible VM's maximum lifespan, making them cost-effective for this workload.
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
A startup's cloud architect reviews their monthly bill and notices costs are higher than expected for a long-running batch job. Switching from on-demand instances to Reserved Instances — or using Spot/Preemptible VMs — can reduce compute costs by up to 72 %. Questions like this test whether you understand the tradeoffs between commitment, flexibility, and cost across cloud pricing models.
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.
Building and operationalizing data processing systems — This question tests Building and operationalizing data processing systems — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Use a cluster with a mix of standard and preemptible VMs. — Option C is correct because preemptible VMs cost about 80% less than standard VMs, and mixing them with standard VMs provides fault tolerance for the job's 6-hour duration. Since the job reads and writes to Cloud Storage (not local HDFS), local SSDs are unnecessary, and a single-node cluster would lack the parallelism needed to process 500 TB efficiently within 6 hours. Using a mix of standard (for critical master/worker nodes) and preemptible VMs (for worker nodes) minimizes cost while ensuring job completion.
What should I do if I get this PDE 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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