VMworld 2016: Extreme Performance: DRS

Session INF8959

300,000 vCenter deployments, 94% with DRS enabled

Quick Facts

• 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.

DRS Faults

• 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.

Observations

• Always right size your VMs
• Occasional swapping is not bad, constant swapping is bad