XK0-006 Troubleshooting Practice Question
A system administrator notices that the server is performing poorly. Running 'vmstat 1 5' shows high 'wa' values. Which subsystem is most likely experiencing a bottleneck?
⚠ Common exam trap
The trap is that candidates see 'wa' and think 'wait' means CPU waiting, so they pick CPU; the exam expects you to know 'wa' is I/O wait, not CPU wait.
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
✓
Disk I/O
In vmstat output, the 'wa' column reports the percentage of CPU time spent waiting for I/O operations to complete. High 'wa' values indicate that the CPU is idle but blocked waiting on disk (or other block device) I/O, which points directly to a disk I/O bottleneck. This is distinct from high 'us' or 'sy' (user/system CPU) or high 'si'/'so' (swap), which would indicate CPU or memory pressure respectively.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Memory
Why it's wrong here
High wa in vmstat measures CPU time spent waiting on I/O completion, not memory pressure; memory bottlenecks appear as high si/so swap activity or low free memory. Memory is tempting because paging to disk can indirectly inflate wait, but that would show as swap-in/swap-out counters, not the wa column itself.
- ✓
Disk I/O
Why this is correct
The wa column in vmstat reports the percentage of CPU time spent idle while waiting for I/O completion. Persistently high wa values indicate processes blocked on storage operations, so the bottleneck lies in the disk I/O subsystem.
- ✗
Network
Why it's wrong here
The wa column reports CPU idle time blocked on disk I/O, so it points at storage, not network throughput or latency. Network is tempting because slow remote storage or NFS can stall processes, but that would surface as socket or retransmission statistics, not the wa field in vmstat.
- ✗
CPU
Why it's wrong here
High wa means the CPU is idle while waiting for I/O, so the processor itself is not the constrained resource; genuine CPU saturation raises us or sy, not wa. CPU is tempting because poor performance often implicates compute, but vmstat separates wait time from actual CPU busy time.
Go deeper
Related to this question
Learn chapter
User and Group Administration
Key term
User
A user is any person, system, or device that interacts with an IT service, resource, or identity system, typically authenticated through credentials and authorized to perform specific actions.
Key term
Output
In IT service management, output is the result or deliverable produced by a process, system, or component, such as data, reports, or services delivered to a customer.
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JA
Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official CompTIA exam blueprint
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