Bigtable Node Sizing: Minimum Nodes for Storage Considering Replication
This PCDE practice question tests your understanding of plan and manage database infrastructure. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. A key principle to apply: storage capacity calculation. 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.
Refer to the exhibit. The company plans to store 3 TB of data in this instance. What is the minimum number of nodes required? (Assume 2 TB per node for HDD and 4 TB per node for SSD; this instance uses SSD.)
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.
The answer is 2 nodes. This is correct because while a single SSD node offers 4 TB of storage—enough to hold the 3 TB dataset—the requirement for replication in a distributed database like Bigtable means you need at least two nodes to provide high availability and durability. With two nodes, each contributing 4 TB of SSD storage, the effective usable capacity after replication is 4 TB (8 TB total divided by 2 replicas), which comfortably accommodates the 3 TB of data while ensuring no single point of failure. On the Google Professional Cloud Database Engineer exam, this question tests your understanding that storage sizing must account for replication overhead, not just raw capacity; a common trap is to pick 1 node based on raw storage alone. Remember the key rule: for minimum nodes with replication, always divide the total raw storage by the replication factor, and never count a single node as meeting high-availability requirements. Memory tip: “One node is a single point of failure; two nodes make a replica pair.”
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
✓
1
The question explicitly assumes 4 TB per SSD node and asks for the minimum number of nodes required to store 3 TB of data. Since 4 TB is greater than 3 TB, a single node provides sufficient raw storage capacity. The question does not specify any requirements for high availability, replication, or redundancy, so the minimum number of nodes is 1.
Key principle: Storage capacity calculation
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
4
Why it's wrong here
4 nodes is excessive; 4 × 4 TB = 16 TB raw storage, far more than needed for 3 TB of data.
✓
1
Why this is correct
Correct. One node provides 4 TB raw storage, which is enough to hold 3 TB of data.
Clue confirmation
The clue word "minimum / minimize" in the question point toward this answer.
Related concept
Storage capacity calculation
✗
2
Why it's wrong here
Two nodes would provide 8 TB raw storage, but the question asks for the minimum. Without HA requirements, one node suffices.
✗
3
Why it's wrong here
Three nodes provide 12 TB raw storage, which is unnecessary for 3 TB of data.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap is that candidates may incorrectly assume that multiple nodes are always required for database instances on Google Cloud, ignoring the explicit assumption that each node provides 4 TB of SSD storage. The question only asks about storage capacity, not high availability or replication.
Detailed technical explanation
How to think about this question
In Couchbase, data is distributed across nodes using vBuckets, and replication is configured at the bucket level (e.g., replica count of 1). With 2 nodes and a replica count of 1, each data item is stored on two nodes, so the total usable storage is (total raw storage) / (number of replicas + 1). For 2 nodes with 4 TB each, raw storage is 8 TB, and with 1 replica, usable storage is 4 TB, which comfortably holds 3 TB. This calculation is critical for capacity planning in distributed NoSQL databases, where replication overhead must be factored in.
KKey Concepts to Remember
Storage capacity calculation
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
Storage capacity calculation
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.
Review storage capacity calculation, then practise related PCDE questions on the same topic to reinforce the concept.
Plan and manage database infrastructure — This question tests Plan and manage database infrastructure — Storage capacity calculation.
What is the correct answer to this question?
The correct answer is: 1 — The question explicitly assumes 4 TB per SSD node and asks for the minimum number of nodes required to store 3 TB of data. Since 4 TB is greater than 3 TB, a single node provides sufficient raw storage capacity. The question does not specify any requirements for high availability, replication, or redundancy, so the minimum number of nodes is 1.
What should I do if I get this PCDE question wrong?
Review storage capacity calculation, then practise related PCDE questions on the same topic to reinforce the concept.
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?
Storage capacity calculation
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