The answer is insufficient buffer allocation for the no-drop class in the QoS policy. In a lossless Fibre Channel fabric, the no-drop class (typically class-fcoe) relies on adequate buffer space to absorb traffic bursts without triggering pause frames or retransmissions. When buffer allocation is too small, the switch cannot handle transient congestion during heavy workloads, causing queuing delays and increased FC latency even though the fabric remains lossless. On the Cisco DCCOR 350-601 exam, this scenario tests your understanding of UCS QoS buffer tuning for storage traffic—a common trap is assuming lossless operation eliminates all latency, when in fact poor buffer provisioning directly causes it. Remember the memory tip: "No-drop needs no-starvation" — if the no-drop class lacks buffer, latency climbs.
350-601 Compute Practice Question
This 350-601 practice question tests your understanding of compute. 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.
An engineer notices that a UCS server with a service profile using a QoS policy for FC traffic experiences excessive latency during heavy workloads. The Fibre Channel fabric is configured for lossless operation. Which design issue is most likely causing the latency?
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.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The QoS policy for FC traffic does not allocate enough buffer for the no-drop class.
The excessive latency during heavy workloads in a lossless Fibre Channel fabric is most likely due to insufficient buffer allocation for the no-drop class in the QoS policy. In UCS, the no-drop class (typically class-fcoe) must have adequate buffer space to prevent frame drops that trigger retransmissions and latency. Without enough buffer, the switch cannot absorb bursts, leading to congestion and increased latency even though the fabric is lossless.
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.
✗
The MTU on the Ethernet uplink from the FI is set to 1500 bytes.
Why it's wrong here
FCoE requires jumbo frames; but this is a QoS policy issue.
✓
The QoS policy for FC traffic does not allocate enough buffer for the no-drop class.
Why this is correct
Insufficient buffer allocation in the no-drop class can cause pause frames and increased latency.
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.
✗
Fibre Channel buffer-to-buffer credit recovery is disabled on the upstream switch.
The vHBA is configured for 16 Gbps but the upstream switch port is 8 Gbps.
Why it's wrong here
This would cause speed mismatch but not necessarily QoS latency.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the misconception that latency in a lossless fabric is caused by external factors like MTU or speed mismatches, rather than the internal QoS buffer allocation for the no-drop class, which is the critical design parameter for FC traffic in UCS.
Detailed technical explanation
How to think about this question
In UCS, the QoS policy for FC traffic defines the no-drop class (class-fcoe) with a dedicated buffer percentage. During heavy workloads, if the buffer is too small, the switch must pause the traffic using priority flow control (PFC) to avoid drops, which introduces latency as frames are held in queues. The buffer allocation is configured via the 'qos policy' in UCS Manager, and the default buffer for the no-drop class may be insufficient for bursty FC traffic, requiring manual tuning based on the expected workload.
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 practitioner preparing for the 350-601 exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.
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.
Compute — This question tests Compute — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The QoS policy for FC traffic does not allocate enough buffer for the no-drop class. — The excessive latency during heavy workloads in a lossless Fibre Channel fabric is most likely due to insufficient buffer allocation for the no-drop class in the QoS policy. In UCS, the no-drop class (typically class-fcoe) must have adequate buffer space to prevent frame drops that trigger retransmissions and latency. Without enough buffer, the switch cannot absorb bursts, leading to congestion and increased latency even though the fabric is lossless.
What should I do if I get this 350-601 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: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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