Quick Answer
The answer is a disk I/O bottleneck. This is correct because the disk queue length consistently above 5 indicates that input/output requests are piling up faster than the storage subsystem can process them, even though CPU and memory utilization remain low. In a virtualized server, a single virtual disk on a RAID 5 array of three mechanical HDDs delivers limited IOPS, so a database workload quickly overwhelms it, causing the long query times. On the CompTIA ITF+ FC0-U61 exam, this scenario tests your ability to distinguish between CPU, memory, and disk bottlenecks using performance counters; a common trap is assuming low CPU usage means no bottleneck, but a high disk queue length points directly to the storage layer. Remember the memory tip: “Queue length above five means the disks are not alive”—if the queue stays over 5, the disks are the bottleneck, not the processor or RAM.
This FC0-U61 practice question tests your understanding of infrastructure. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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 hospital's IT team manages a virtualized server hosting a patient records database. The server has one physical processor with 6 cores, 32 GB of RAM, and a RAID 5 array of three 1 TB HDDs. The virtual machine (VM) running the database is configured with 2 vCPUs, 8 GB RAM, and a 500 GB virtual disk stored on the RAID array. Users report that database queries are taking much longer than usual. The host server shows CPU utilization at 20%, memory at 60%, and the disk queue length frequently stays above 5. Which of the following is the most likely cause of the performance issue?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Disk I/O bottleneck
A high disk queue length indicates that the storage subsystem is overloaded, causing slow response times.
Network bandwidth limitation
Why wrong: No network issues are reported or observed.
Insufficient memory
Why wrong: Memory usage is 60%, leaving ample headroom.
Insufficient CPU resources
Why wrong: CPU utilization is only 20%, so the CPU is not a bottleneck.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
Disk I/O bottleneck
The disk queue length consistently exceeding 5 indicates that I/O requests are waiting for the storage subsystem, which is a classic sign of a disk I/O bottleneck. The RAID 5 array of three 1 TB HDDs provides limited IOPS compared to SSDs, and the single virtual disk on this array cannot keep up with the database workload. Even though CPU and memory utilization are moderate, the high queue length shows the disks are the limiting factor.
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.
Disk I/O bottleneck
Why this is correct
A high disk queue length indicates that the storage subsystem is overloaded, causing slow response times.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
Network bandwidth limitation
Why it's wrong here
No network issues are reported or observed.
Insufficient memory
Why it's wrong here
Memory usage is 60%, leaving ample headroom.
Insufficient CPU resources
Why it's wrong here
CPU utilization is only 20%, so the CPU is not a bottleneck.
Common exam traps
CompTIA often tests the misconception that high disk queue length is always caused by insufficient memory, but here memory is adequate and the queue is due to slow HDDs in RAID 5, not paging.
Detailed technical explanation
RAID 5 with three HDDs offers read performance close to (n-1) times a single drive but write performance is penalized due to parity calculations, especially with small random I/O typical of databases. The disk queue length metric in Windows Performance Monitor or Linux iostat reflects the number of I/O requests waiting to be serviced; a sustained value above 2 per spindle often indicates saturation. In virtualized environments, the hypervisor's storage stack can add further latency if the underlying RAID controller or HBA is overwhelmed.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
A small business has 20 workstations on the 192.168.1.0/24 network and one public IP from its ISP. The router uses PAT (NAT overload) so all 20 devices share one public address using different source ports. NAT questions test whether you understand the four address terms and which direction each translation applies.
What to study next
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FAQ
Infrastructure — This question tests Infrastructure — Read the scenario before looking for a memorised answer..
The correct answer is: Disk I/O bottleneck — The disk queue length consistently exceeding 5 indicates that I/O requests are waiting for the storage subsystem, which is a classic sign of a disk I/O bottleneck. The RAID 5 array of three 1 TB HDDs provides limited IOPS compared to SSDs, and the single virtual disk on this array cannot keep up with the database workload. Even though CPU and memory utilization are moderate, the high queue length shows the disks are the limiting factor.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 30, 2026
This FC0-U61 practice question is part of Courseiva's free CompTIA 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 FC0-U61 exam.
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