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.


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


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