Quick Answer
The answer is SSD persistent disk. This is the correct choice because SSD persistent disk delivers consistent low-latency performance essential for high random read/write workloads, offering significantly higher IOPS and throughput than HDD or balanced persistent disks, which is critical for MySQL databases on Cloud SQL where random I/O patterns dominate. On the Google Professional Cloud Database Engineer exam, this question tests your understanding of Cloud SQL storage options and their performance characteristics under different workload profiles; a common trap is selecting balanced persistent disk for its cost savings, but that tier sacrifices the predictable latency required for transactional databases. Remember the mnemonic “SSD for Speed, HDD for Heaps” — SSD persistent disk is your go-to when random read/write performance is the priority, while HDD is only suitable for sequential, low-IOPS workloads.
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. 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 is running a MySQL database on Cloud SQL and needs to optimize for high random read/write performance. Which storage type should they choose?
SSD persistent disk
SSD persistent disk offers high IOPS and low latency, ideal for database storage in Cloud SQL.
Local SSD
Why wrong: Local SSD is not supported for Cloud SQL instances; it is used with Compute Engine.
Balanced persistent disk
Why wrong: Balanced persistent disk provides moderate performance but is not as fast as SSD.
HDD persistent disk
Why wrong: HDD provides lower IOPS and is not optimal for random read/write workloads.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
SSD persistent disk
SSD persistent disk provides consistent low-latency performance for random read/write operations, which is critical for MySQL databases on Cloud SQL. It offers higher IOPS and throughput compared to HDD or balanced persistent disks, making it the optimal choice for high random read/write workloads.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
SSD persistent disk
Why this is correct
SSD persistent disk offers high IOPS and low latency, ideal for database storage in Cloud SQL.
Related concept
Read the scenario before looking for a memorised answer.
Local SSD
Why it's wrong here
Local SSD is not supported for Cloud SQL instances; it is used with Compute Engine.
Balanced persistent disk
Why it's wrong here
Balanced persistent disk provides moderate performance but is not as fast as SSD.
HDD persistent disk
Why it's wrong here
HDD provides lower IOPS and is not optimal for random read/write workloads.
Common exam traps
The trap here is that candidates may confuse Local SSD's high performance with persistence, not realizing it is ephemeral and cannot be used for Cloud SQL's managed database service, which requires durable storage.
Detailed technical explanation
SSD persistent disks use solid-state storage with a block-level interface that delivers consistent IOPS regardless of disk size, with a baseline of 0.3 IOPS/GB and burst capabilities up to 30,000 IOPS. For MySQL, random I/O performance is critical for operations like index scans and row lookups, where SSD persistent disks reduce latency to single-digit milliseconds compared to HDD's tens of milliseconds. In real-world scenarios, a high-traffic e-commerce application using MySQL on Cloud SQL would see query response times degrade significantly if HDD or balanced disks were used instead of SSD.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
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
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FAQ
Plan and manage database infrastructure — This question tests Plan and manage database infrastructure — Read the scenario before looking for a memorised answer..
The correct answer is: SSD persistent disk — SSD persistent disk provides consistent low-latency performance for random read/write operations, which is critical for MySQL databases on Cloud SQL. It offers higher IOPS and throughput compared to HDD or balanced persistent disks, making it the optimal choice for high random read/write workloads.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 25, 2026
This PCDE 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 PCDE exam.
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