What metrics are considered when Acropolis Dynamic Scheduling makes a migration decision on AHV related to CPU usage? Does ADS consider only CPU usage on the Host? Or does ADS take into consideration other VM or Host metrics such as CPU Ready, Co Stop, and/or Steal Time?
Best answer by Moustafa HindawiView original
ADS monitors the following resources:
ADS does not monitor memory and networking usage.
How Acropolis Dynamic Scheduling Works
Lazan is the ADS service in an AHV cluster. AOS selects a Lazan manager and Lazan solver among the hosts in the cluster to effectively manage ADS operations.
ADS performs the following tasks to resolve compute and storage I/O contentions or hotspots:
- The Lazan manager gathers statistics from the components it monitors.
- The Lazan solver (runner) checks the statistics for potential anomalies and determines how to resolve them, if possible.
- The Lazan manager invokes the tasks (for example, VM migrations) to resolve the situation.
When Is a Hotspot Detected?
Lazan runs every 15 minutes and analyzes the resource usage for at least that period of time. If the resource utilization of an AHV host remains >85% for the span of 15 minutes, Lazan triggers migration tasks to remove the hotspot.
Note: For a storage hotspot, ADS looks at the last 40 minutes of data and uses a smoothing algorithm to use the most recent data. For a CPU hotspot, ADS looks at the last 10 minutes of data only, that is, the average CPU usage over the last 10 minutes.
Following are the possible reasons if there is an obvious hotspot, but the VMs did not migrate:
In these situations, the other hosts cannot accommodate the large VM without causing contention there as well. Lazan does not prioritize one host or VM over others for contention, so it leaves the VM where it is hosted.
If the cluster has an RF2 configuration, the cluster must have a minimum of two all-flash nodes for successful migration of VMs on all the all-flash nodes.