Why is a workload's latency high when the IOPS are low?
Applies to
- ONTAP 9
- Clustered Data ONTAP 8
- Data ONTAP 7-mode
Answer
ONTAP will respond to requests as they come in, and a workload that has few requests will appear to be higher but be responding perfectly fine.Additional Information
- Definitions:
- mean: average, or the sum of all instance values divided by number of instances
- median: the instance value in the middle when values are ordered from smallest to largest
- mode: the instance value occurring most often
- In the statistics branch of math, you need to use mean, median, and mode to help calculate that.
Example 1: Latency observed across 3 instances in a period (say 3 ops in a minute): 1 ms, 100 ms, 1 ms
- mean: (1+100+1)/3=34 ms
- median: 1ms
- mode: 1 ms
- ONTAP will often give average latency, but in this case, the median and mode show that latency is actually really good.
Example 2: Latency observed across 20 instances (7 ops/second): 1ms, 1ms, 1ms, 1ms, 100ms, 1ms, 1ms...1ms (19 @ 1 ms, 1@100 ms)
- mean: (19+100) /20=5.95ms
- median: 1 ms
- mode: 1 ms
- In this case, average latency is more accurate than the prior example because we have enough data to have better confidence in the numbers
How to identify a client, network, or ONTAP problem calculating concurrency