Quick Answer
The answer is a port speed mismatch between the server and the tape library. In Fibre Channel, each link negotiates its own speed independently, and the end-to-end throughput is always constrained by the slowest link in the data path. Even though the backup server can transmit at 8 Gbps, the tape library’s 4 Gbps receive port creates a hard bottleneck that caps the backup performance at 4 Gbps, regardless of hardware compression. On the Cisco DCCOR 350-601 exam, this scenario tests your understanding of Fibre Channel flow control and the principle that link speed mismatches directly limit throughput, not compression or buffer credits. A common trap is assuming hardware compression compensates for a slower link—it does not, because compression reduces data volume on tape but cannot increase the physical line rate. Remember the memory tip: “The chain is only as fast as its slowest port.”
This 350-601 practice question tests your understanding of storage network. 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 network engineer is troubleshooting a slow backup performance between a backup server and a tape library connected via FC. The backup server is connected to a Cisco MDS switch at 8 Gbps, and the tape library is connected at 4 Gbps. The backup job is using hardware compression. Which factor is most likely limiting performance?
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.
Port speed mismatch between the server and tape library
The slower device (4 Gbps) determines the link speed.
Insufficient buffer credits on the MDS switch
Why wrong: Buffer credits affect long-distance links, not speed-limited performance.
Hardware compression on the tape library
Why wrong: Compression reduces data, improving performance, not limiting it.
Half-duplex mode on the FC link
Why wrong: FC always operates in full-duplex mode.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
Port speed mismatch between the server and tape library
The backup server is connected at 8 Gbps while the tape library is connected at 4 Gbps. In Fibre Channel, the link speed is negotiated per port, and the end-to‑end flow is limited by the slowest link in the path. Even though the server can transmit at 8 Gbps, the tape library can only receive at 4 Gbps, creating a bottleneck that caps the backup throughput. Hardware compression on the tape library does not cause this speed mismatch; it actually reduces the amount of data written to tape, but the physical link rate remains 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.
Port speed mismatch between the server and tape library
Why this is correct
The slower device (4 Gbps) determines the link speed.
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.
Insufficient buffer credits on the MDS switch
Why it's wrong here
Buffer credits affect long-distance links, not speed-limited performance.
Hardware compression on the tape library
Why it's wrong here
Compression reduces data, improving performance, not limiting it.
Half-duplex mode on the FC link
Why it's wrong here
FC always operates in full-duplex mode.
Common exam traps
Cisco often tests the misconception that buffer credits are the primary cause of any FC performance issue, but here the persistent throughput limit is due to a static speed mismatch, not a dynamic credit starvation problem.
Detailed technical explanation
Fibre Channel uses credit‑based flow control (buffer‑to‑buffer credits) to manage frame delivery, but the physical line rate is negotiated independently on each port. When a faster transmitter sends to a slower receiver, the receiver’s buffer credits will be consumed quickly, forcing the transmitter to pause (R_RDY flow control), which effectively throttles throughput to the slower link speed. In real‑world backup environments, this mismatch is often overlooked because both ends show ‘link up’ at their respective speeds, but the actual data rate is limited by the slowest hop.
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
Storage Network — This question tests Storage Network — Read the scenario before looking for a memorised answer..
The correct answer is: Port speed mismatch between the server and tape library — The backup server is connected at 8 Gbps while the tape library is connected at 4 Gbps. In Fibre Channel, the link speed is negotiated per port, and the end-to‑end flow is limited by the slowest link in the path. Even though the server can transmit at 8 Gbps, the tape library can only receive at 4 Gbps, creating a bottleneck that caps the backup throughput. Hardware compression on the tape library does not cause this speed mismatch; it actually reduces the amount of data written to tape, but the physical link rate remains 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 11, 2026
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