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Design and Plan Database Solutions →hardMultiple ChoiceObjective-mapped

PCDOE Design and Plan Database Solutions Practice Question

This PCDOE practice question tests your understanding of design and plan database solutions. 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.

You need to size a Bigtable cluster for a workload that requires 50,000 reads per second (QPS) and 20,000 writes per second. Each read is about 1 KB, each write is about 1 KB. The data volume is 5 TB and growing. You choose SSD storage. What is the minimum number of nodes?

Clue words in this question

Noticing these words before you look at the options changes how you read each choice.

  • Clue: "minimum / minimize"

    Why it matters: Asks for the least resource use — fewest addresses, smallest subnet, lowest overhead. Eliminate over-provisioned options even if they would technically work.

Answer choices

Why each option matters

Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.

Correct answer & explanation

✓

72 nodes

The correct answer is A (72 nodes) because Bigtable's SSD nodes provide approximately 10,000 read QPS per node (for 1 KB reads) and 10,000 write QPS per node (for 1 KB writes). With 50,000 reads and 20,000 writes, the read requirement dominates, needing 5 nodes for reads, but writes require 2 nodes. However, Bigtable's architecture requires a minimum of 3 nodes for replication and availability, and the total throughput must be scaled to account for node overhead and growth. The calculation: (50,000 reads / 10,000) = 5 nodes for reads, (20,000 writes / 10,000) = 2 nodes for writes, but the combined load and Bigtable's recommendation for SSD nodes (each handling ~1,000 QPS per core, with 30 cores per node) yields 72 nodes when factoring in the 5 TB data volume (each SSD node stores ~70 GB usable) and growth.

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.

  • ✓

    72 nodes

    Why this is correct

    Storage requirement (5000 GB / 70 GB per node = 71.4, rounded up to 72) dictates the node count.

    Clue confirmation

    The clue word "minimum / minimize" in the question point toward this answer.

    Related concept

    Read the scenario before looking for a memorised answer.

  • ✗

    50 nodes

    Why it's wrong here

    Insufficient storage; 50 nodes provide 3500-5000 GB, but 5 TB = 5120 GB, so not enough.

  • ✗

    7 nodes

    Why it's wrong here

    Does not account for storage needs.

  • ✗

    5 nodes

    Why it's wrong here

    Sufficient for reads but insufficient for storage.

Common exam traps

Common exam trap: answer the scenario, not the keyword

Cisco often tests the misconception that you can size Bigtable nodes based solely on QPS without considering data volume and replication overhead, leading candidates to pick a lower node count like 5 or 7.

Detailed technical explanation

How to think about this question

Bigtable's SSD nodes have a throughput limit of approximately 10,000 QPS for mixed 1 KB reads and writes, but this is a guideline; actual performance depends on row key design, locality groups, and compaction overhead. The 5 TB data volume with SSD storage requires careful node count because each SSD node provides about 70 GB of usable storage after replication (3x replication factor), meaning 5 TB / 70 GB ≈ 72 nodes for storage alone, which coincidentally matches the throughput requirement. In real-world scenarios, you must also consider CPU utilization for compaction and garbage collection, which can reduce effective throughput by 20-30%.

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 media company stores terabytes of video archives that are accessed once a year for audit purposes. Moving these objects to a cold storage tier (Azure Archive, S3 Glacier, or Google Nearline) costs a fraction of hot storage. Questions like this test whether you understand storage tiers, access frequency tradeoffs, and retrieval latency requirements.

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.

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FAQ

Questions learners often ask

What does this PCDOE question test?

Design and Plan Database Solutions — This question tests Design and Plan Database Solutions — Read the scenario before looking for a memorised answer..

What is the correct answer to this question?

The correct answer is: 72 nodes — The correct answer is A (72 nodes) because Bigtable's SSD nodes provide approximately 10,000 read QPS per node (for 1 KB reads) and 10,000 write QPS per node (for 1 KB writes). With 50,000 reads and 20,000 writes, the read requirement dominates, needing 5 nodes for reads, but writes require 2 nodes. However, Bigtable's architecture requires a minimum of 3 nodes for replication and availability, and the total throughput must be scaled to account for node overhead and growth. The calculation: (50,000 reads / 10,000) = 5 nodes for reads, (20,000 writes / 10,000) = 2 nodes for writes, but the combined load and Bigtable's recommendation for SSD nodes (each handling ~1,000 QPS per core, with 30 cores per node) yields 72 nodes when factoring in the 5 TB data volume (each SSD node stores ~70 GB usable) and growth.

What should I do if I get this PCDOE question wrong?

Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.

Are there clue words in this question I should notice?

Yes — watch for: "minimum / minimize". Asks for the least resource use — fewest addresses, smallest subnet, lowest overhead. Eliminate over-provisioned options even if they would technically work.

What is the key concept behind this question?

Read the scenario before looking for a memorised answer.

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Last reviewed: Jul 4, 2026

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This PCDOE practice question is part of Courseiva's free Google Cloud certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the PCDOE exam.