VMworld 2013: vSphere 5.5 DRS New Features, Future Directions

image_thumb1 This is my first technical session of VMworld 2013, VSVC5280. It covered new vSphere 5.5 DRS features, explained why DRS may not always “perfectly” balance your cluster. vSphere 5.5 has a lot of new storage features, and DRS has been enhanced to be aware of VSAN and vFlash technologies. As always during conferences I’m real time blogging, so I may not have caught all of the details and don’t have time to expound on the new features. Stay tuned for future blog posts on vSphere 5.5 goodness.

Session Outline:

  • Advanced resource mgt concepts
  • New features in vSphere 5.5
  • Integrate with new storage and networking features
  • Future directions

Advanced Resource Management Concepts

  • DRS treats the cluster as one giant host
  • Capacity of this “host” = capacity of the cluster
  • Main issue: Fragmentation of resource across hosts
  • Primary goal: Keep VMs happy by meeting their resource demands
  • Why meet VM demand as the primary goal? VM demand satisfied  makes VM or applications happy
  • Why is this not met by default? Host overload
  • Three ways to find more cluster capacity: Reclaim resources, migrate VMs, Power on a host (if DPM enabled)
  • Demand does NOT equal current utilization
  • Why not load balance the DRS cluster as the primary goal? Load balancing is NOT free. Movement has a cost.
  • Load balancing is a mechanism used to meet VM demands. If VM resources are being met, don’t move the VM.

DRS Load-Balancing: The balls and the Bins Problem

  • Problem: Assign n balls to m bins
  • Key challenges: Dynamic numbers and sizes of bins/balls
  • Constraints of on co-location, placement and others
  • VM resource entitlements are the “balls” and Host resources at the “bins”
  • Dynamic load, dynamic capacity

Goals of DRS Load-Balancing

  • Fairly distribute VM demand
  • Enforce constraints
  • Recommend moves that improve balance
  • Recommend moves with long term benefits

The Myth of Target Balance

  • UI slider tells us which star threshold is acceptable
  • Implicit target number of cluster imbalance metric
  • Constraints can make it hard to meet target balance
  • If all your VMs are happy, a little imbalance is FINE

vSphere 5.5 New Features

  • In vSphere 5.1 there is a new option: LimitVMsPerESXhost  – DRS will not admit or migrate more than x VMs to any host
  • In vSphere 5.5 LimitVMsPerESXHostPercent
  • Limit VMs per host limit: Example: Mean = 8, Buffer % 50, new limit is 12 (50% * 8)
  • New: Latency-sensitive VMs and DRS. New GUI pulldown option
  • Magical “soft affinity” rule to the current host, for workloads that may be sensitive to vMotions

CPU Ready Time Overview

  • Amount of time the vCPU waits to run but before it can be scheduled on a pCPU. Measures CPU contention.
  • Many causes for high ready time, many fixes, many red-herrings
  • “%RDY is 80, that can NOT be good”: Cumulative number, so divide by number of cores.
  • Rule of thumb: Up to 5% per vCPU is usually alright
  • “Host utilization is very low, %RDY is very high”: Host power management reduces pCPU capacity
  • Set BIOS option to “OS control” and let ESX decide
  • Low VM or RP CPU limit values restrict cycles delivered to VMs. “Set your VMs free” by not configuring MHz limits
  • NUMA Scheduling effects: NUMA scheduler can increase %RDY time
  • Application performance is often better because NUMA scheduler optimizes memory performance

Better Handling in DRS

  • vSphere 5.5 new feature: AggressiveCPUActive=1
  • Only use for very spiky workloads that the 5 minute average may not catch
  • vSphere 5.5: PercentIndleMBInMemDemand – Handles memory bursting protection

New Storage and Networking Features

  • vFlash: Initial DRS placement just works
  • DRS load balancing treats VMs as it soft-affinity to current host
  • VMs will not migrate unless absolutely necessary
  • Host maintenance mode may take longer
  • vFlash space can get fragemented across the cluster
  • vMotions may take longer

VSAN interop with SRS

  • DRS is completely compatible with VSAN

Autoscaling Proxy Switch Ports and DRS

  • DRS admission control – proxy switch port test
  • Makes sure host has enough ports on proxy switch: vNIC ports, uplink pots, vmkernel ports
  • In vSphere 5.1 per ports per host = 4096
  • Host will power on no more than 400 VMs
  • New to vSphere 5.5: Autoscaling switch ports

Future Directions

  • Per-vNIC bandwidth reservations
  • pNIC capacity at host will be pooled together
  • Static overhead memory – influenced by VM Config parameters, VMware features, ESXi build number
  • Overhead memory: This value is used in admission control and DRS load balancing
  • Better estimation of these numbers leads to higher consolidation during power-on

Proactive DRS – Possible future features

  • Lifecycle: Monitor, predict, remediate, compute, evaluate
  • Imagine a vMotion happening before a workload spike
  • Predict and avoid spikes
  • make remediation cheaper
  • Proactive load-balancing
  • Proactive DPM – Power on hosts before capacity is needed
  • use predicted data for placement, evacuation
  • vCOPS integration to perform analytics and capacity planning
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