CPU/Memory reservation for DD VE in VMware and impact on HA cluster

When DD VE is deployed in VMware, we recommend CPU and memory reservations with DD VE 2.0 to ensure right level of performance. We provide this as part of the OVA deployment configuration as well. Users need to be aware that if a VM has memory reservation it will have impacts on the resource slot calculation for HA cluster. Here is a VMware document which explains this -

VMware host failures clusters admission control policy

Here is an excerpt from the document

Slot Size Calculation

Slot size is comprised of two components, CPU and memory.

■ vSphere HA calculates the CPU component by obtaining the CPU reservation of each powered-on virtual machine and selecting the largest value. If you have not specified a CPU reservation for a virtual machine, it is assigned a default value of 32MHz. You can change this value by using the das.vmcpuminmhz advanced attribute.)

■ vSphere HA calculates the memory component by obtaining the memory reservation, plus memory overhead, of each powered-on virtual machine and selecting the largest value. There is no default value for the memory reservation.

If your cluster contains any virtual machines that have much larger reservations than the others, they will distort slot size calculation. To avoid this, you can specify an upper bound for the CPU or memory component of the slot size by using the das.slotcpuinmhz or das.slotmeminmb advanced attributes, respectively. See vSphere HA Advanced Attributes.

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