- A
Verify that EBS optimization is enabled
Why wrong: EBS optimization is enabled by default on large instances and likely not the issue.
- B
Increase the SWAP space on the instance
Why wrong: SAP HANA should not use SWAP; it relies on memory.
- C
Upgrade to a compute-optimized instance like c5.24xlarge
Why wrong: Compute-optimized instances have less memory, unsuitable for HANA.
- D
Check the Elastic Network Adapter (ENA) settings and consider tuning the ring buffer size
Tuning ENA can improve network throughput, which may be the bottleneck for I/O bound operations.
Question 1,422 of 1,733
Tuning ENA Ring Buffer for SAP HANA on AWS
This PAS-C01 practice question tests your understanding of design of sap workloads on aws. 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 SAP administrator is troubleshooting a performance issue on an SAP HANA database running on an r5.24xlarge instance. The database is I/O bound during high load periods. The administrator has already verified that the EBS volumes are not saturated. What should the administrator check next?
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
✓
Check the Elastic Network Adapter (ENA) settings and consider tuning the ring buffer size
The correct answer is D because on an r5.24xlarge instance, EBS optimization is always enabled by default, so verifying it again is unnecessary. The issue is I/O bound during high load, but EBS volumes are not saturated, indicating the bottleneck is likely at the network layer. The Elastic Network Adapter (ENA) ring buffer size can become overwhelmed under high network traffic, causing packet drops and increased latency, which manifests as I/O wait. Tuning the ring buffer size (e.g., using `ethtool -G eth0 rx 4096 tx 4096`) can reduce drops and improve throughput for SAP HANA's network-intensive operations.
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.
- ✗
Verify that EBS optimization is enabled
Why it's wrong here
EBS optimization is enabled by default on large instances and likely not the issue.
- ✗
Increase the SWAP space on the instance
Why it's wrong here
SAP HANA should not use SWAP; it relies on memory.
- ✗
Upgrade to a compute-optimized instance like c5.24xlarge
Why it's wrong here
Compute-optimized instances have less memory, unsuitable for HANA.
- ✓
Check the Elastic Network Adapter (ENA) settings and consider tuning the ring buffer size
Why this is correct
Tuning ENA can improve network throughput, which may be the bottleneck for I/O bound operations.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates assume EBS optimization must be manually verified or enabled, but on modern Nitro-based instances like r5, it is always active, so the real bottleneck is often the network adapter configuration.
Detailed technical explanation
How to think about this question
The ENA ring buffer is a kernel-level queue that holds incoming network packets before they are processed by the driver. When the ring buffer is too small, packets are dropped (as seen in `ethtool -S eth0` under `rx_missed_errors`), causing TCP retransmissions and increased latency. For SAP HANA, which relies on high-throughput network I/O for replication and client communication, even small packet drops can degrade performance. Tuning the ring buffer size (e.g., to 4096 entries) can reduce drops by up to 90% in high-throughput scenarios, as documented in AWS networking best practices.
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
An e-commerce site experiences heavy traffic on Black Friday and near-zero traffic during off-peak weeks. Rather than provisioning permanent large VMs, the team uses auto-scaling groups that add capacity automatically under load and reduce it overnight. Questions like this test whether you understand elasticity, availability zones, and cloud compute scaling patterns.
Quick reference
OSI Model Reference
| Layer | Name | PDU | Key Protocols / Devices |
|---|---|---|---|
| 7 | Application | Data | HTTP, HTTPS, DNS, SMTP, FTP, SSH |
| 6 | Presentation | Data | TLS / SSL, JPEG, ASCII encoding |
| 5 | Session | Data | NetBIOS, RPC, SIP |
| 4 | Transport | Segment / Datagram | TCP, UDP |
| 3 | Network | Packet | IP, ICMP, OSPF — Routers |
| 2 | Data Link | Frame | Ethernet, Wi-Fi, PPP — Switches, Bridges |
| 1 | Physical | Bits | Cables, NICs, Hubs, Repeaters |
What to study next
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FAQ
Questions learners often ask
What does this PAS-C01 question test?
Design of SAP Workloads on AWS — This question tests Design of SAP Workloads on AWS — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Check the Elastic Network Adapter (ENA) settings and consider tuning the ring buffer size — The correct answer is D because on an r5.24xlarge instance, EBS optimization is always enabled by default, so verifying it again is unnecessary. The issue is I/O bound during high load, but EBS volumes are not saturated, indicating the bottleneck is likely at the network layer. The Elastic Network Adapter (ENA) ring buffer size can become overwhelmed under high network traffic, causing packet drops and increased latency, which manifests as I/O wait. Tuning the ring buffer size (e.g., using `ethtool -G eth0 rx 4096 tx 4096`) can reduce drops and improve throughput for SAP HANA's network-intensive operations.
What should I do if I get this PAS-C01 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
Same concept, more angles
1 more ways this is tested on PAS-C01
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. An SAP system on AWS is running on an r5.16xlarge instance. The system is experiencing network throughput bottlenecks. Which step should be taken to improve network performance?
medium- A.Move the instance to a placement group
- B.Attach an Elastic Fabric Adapter
- ✓ C.Enable Enhanced Networking and install the ENA driver
- D.Change the instance type to c5.18xlarge
Why C: Option C is correct because enabling Enhanced Networking and installing the Elastic Network Adapter (ENA) driver is the standard method to achieve higher packet-per-second (PPS) performance, lower latency, and increased network bandwidth on supported instance types like r5.16xlarge. Without the ENA driver, the instance uses the older Xen network driver, which cannot utilize the full 25 Gbps network bandwidth available to r5 instances, leading to throughput bottlenecks.
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Last reviewed: Jun 24, 2026
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