300,000 vCenter deployments, 94% with DRS enabled
- Faster power on for large clusters: 6.5 is 3x faster than 5.5 and 6.0.
- 5x lower CPU utilization in 6.5 than previous versions
- 6.5 has better VM placements
DRS ensures resource availability – DRS does this in two ways
- Effective initial placement – Use the right host
- Efficient load balancing – Moving VMs to different hosts
- DRS collects 20 VM performance metrics and 5 host metrics – CPU ready time, memory swapped, memory active, shared memory, CPU used max, CPU used average
- Application performance is the primary goal of DRS
Factors Impacting DRS Performance
- Migration threshold – Left makes it less aggressive
- Rules — Too many rules may prevent DRS balancing the cluster
- Reservations, limits, shares – Do not set reservations unless absolutely necessary
- VM Overrides – Custom DRS settings for a VM.
- When DRS tries to fix something, but can’t.
DRS Performance Case Studies
- Case 1: How does DRS react to spikes in workload? DRS reacts to spikes and will move loads.
- Case 2: Does DRS prefer moving heavy or light VMs? DRS prefers to move medium workloads to restore balance faster.
- Case 3: Why is memory utilization not balanced? DRS considers active memory+ 25% of idle memory. It will not perfectly “balance” memory across all hosts.
- Always right size your VMs
- Occasional swapping is not bad, constant swapping is bad