NS0-157 · Question #87
A customer has LUNs that are being accessed through iSCSI. The applications have experienced increased LUN latency over the last couple of days. Which two components should you review to determine…
The correct answer is A. node CPU utilization C. Ethernet network performance. iSCSI LUN latency is affected by the processing node's CPU load and the underlying Ethernet network, since iSCSI is an IP-based protocol that runs entirely over Ethernet infrastructure.
Question
A customer has LUNs that are being accessed through iSCSI. The applications have experienced increased LUN latency over the last couple of days. Which two components should you review to determine what caused the rise in latency? (Choose two.)
Options
- Anode CPU utilization
- BFC switch performance
- CEthernet network performance
- Dcluster management switch performance
How the community answered
(28 responses)- A71% (20)
- B18% (5)
- D11% (3)
Why each option
iSCSI LUN latency is affected by the processing node's CPU load and the underlying Ethernet network, since iSCSI is an IP-based protocol that runs entirely over Ethernet infrastructure.
The storage node's CPU handles iSCSI protocol processing, LUN request queuing, and ONTAP scheduling - high CPU utilization can directly delay the processing of iSCSI commands and increase LUN response times.
FC switch performance is irrelevant for iSCSI because iSCSI uses Ethernet and TCP/IP, not Fibre Channel - FC switches carry FCP traffic, not iSCSI traffic.
iSCSI encapsulates SCSI commands over TCP/IP and is transported over Ethernet, so congestion, packet loss, retransmissions, or high latency on the Ethernet network will directly translate into elevated LUN latency seen by the application.
The cluster management switch carries only out-of-band management traffic such as SSH and HTTPS sessions and has no role in carrying iSCSI data traffic, so its performance does not affect LUN latency.
Concept tested: iSCSI LUN latency troubleshooting - CPU and Ethernet impact
Source: https://docs.netapp.com/us-en/ontap/san-admin/iscsi-concept.html
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