350-601 Compute Practice Question
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?
⚠ Common exam trap
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.
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
✓
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.
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.
- ✗
Fibre Channel buffer-to-buffer credit recovery is disabled on the upstream switch.
Why it's wrong here
Not directly related to QoS buffer allocation.
- ✗
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.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 350-601 practice question is part of Courseiva's free Cisco 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 350-601 exam.