5 Whys that very helpful for a support service company to identify the root cause of any incident or issues.

1. 5 Whys

2. “ไอน์สไตน์เคยพูดไว้ว่า.. ถ้าเค้ามีเวลา 1 ชั่วโมงในการแก้ไขปัญหา เค้า
จะใช้เวลา 55นาที กับการมองที่ปัญหา ส่วนอีก 5นาทีที่เหลือค่อยมองถึง
หนทางในการแก้ไข”
“If I had an hour to solve a problem I’d spend 55
minutes thinking about the problem and 5
minutes thinking about solutions.”

4. 5 Whys
Key Points
The 5 Whys strategy is a simple, effective tool for uncovering
the root of a problem. You can use it in troubleshooting,
problem-solving, and quality-improvement initiatives.
Start with a problem and ask why it is occurring. Make sure
that your answer is grounded in fact, and then ask the
question again. Continue the process until you reach the root
cause of the problem, and you can identify a counter-
measure that will prevent it from recurring.
Bear in mind that this questioning process is best suited to
simple or moderately difficult problems. Complex problems
may benefit from a more detailed approach, although using 5
Whys will still give you useful insights.

5. Why cannot access VM on ab21345 ?
1
Because there ESXi was hang and error

6. Why ESXi hang?
2
Because there services Large Receive Offload (LRO) was error

7. Why LRO error ?
Because there sub-services vmxnet3 was error
3

8. Why vmxnet3 error ?
Because know issue (BUG) in V6.0 the interger overflow in vmxnet3
backend which leads to PSOD under certain condition.
4

9. Why integer overflow in vmxnet?
LRO reassembles incoming network packets into larger buffers and
transfers the resulting larger but fewer packets to the network stack
of the host or virtual machine. The CPU has to process fewer packets
than when LRO is disabled, which reduces its utilization for
networking.
5