A cluster component can be in contention when it is being over-used by one or more workloads. A QoS policy group can be in contention when workload activity exceeds a configured limit and the workloads are being throttled.
A component that is in contention cannot perform at an optimal level, its performance has declined, and the performance of other cluster components and workloads, called victims, might be impacted. To bring a component out of contention, you need to reduce its workload or increase its ability to handle more work, so that the performance can return to normal levels. Because Performance Manager collects and analyzes workload activity in 5 minute intervals, it only detects when a cluster component is consistently over-used, but does not detect transient spikes of over-usage.
For example, a storage aggregate may be under contention because one or more workloads on it are competing for their I/O requests to be fulfilled. Other workloads on the aggregate can be impacted, causing their performance to decrease. To reduce the amount of activity on the aggregate, there are different steps you can take, such as moving one or more workloads to a less busy aggregate, to lessen the overall workload demand on the current aggregate. For a QoS policy group, you can adjust the throughput limit, or move workloads to a different policy group, so that the workloads are no longer being throttled.