What is the most likely cause of this behavior?

A storage administrator is investigating non-linear variations in throughput when zoning additional hosts to certain front-end adapters. They notice a certain performance characteristic having 10 identical hosts zoned to the same FA ports. After adding the 11th host, the throughput sometimes drops more than 20%.

What is the most likely cause of this behavior?
A . Average disk queue length on the hosts exceed 3
B . I/O sizes over 128 KiB are being used on the hosts
C . QFULL responses of the FA ports
D . System Write Pending > 75%

View Answer

Answer: C

Explanation:

The most likely cause of this behavior is QFULL responses of the FA ports. When additional hosts are zoned to certain front-end adapters, the FA ports may not be able to handle the increased I/O requests, resulting in QFULL responses. This can cause non-linear variations in throughput and sometimes a drop in throughput of more than 20%.

Reference: Dell EMC PowerMax: Service Levels for PowerMaxOS