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VCAP-DCA Study notes – 3.2 Optimise Virtual Machine resources

This objective is focused on the VMs rather than the hosts but there’s still a large overlap between this objective and the previous one.


  • Compare and contrast virtual and physical hardware resources
  • Identify VMware memory management techniques
  • Identify VMware CPU load balancing techniques
  • Identify pre?requisites for Hot Add features

Skills and Abilities

  • Calculate available resources
  • Properly size a Virtual Machine based on application workload
  • Configure large memory pages
  • Understand appropriate use cases for CPU affinity

Tools & learning resources

Identify memory management techniques

The theory – read the following blogposts;

The following memory mechanisms were covered in section 3.1 so I won’t duplicate;

  • transparent page sharing
  • ballooning (via VMTools)
  • memory compression (vSphere 4.1 onwards)
  • virtual swap files
  • NUMA

There are also various mechanisms for controlling memory allocations to VMs;

  • reservations and limitations
  • shares – disk, CPU and memory
  • resource pools (in clusters)

Disable unnecessary devices in the VM settings (floppy drive, USB controllers, extra NICs etc) as they have a memory overhead.

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