Vmware Slot Size
Slot Size Calculation Slot size is comprised of two components, CPU and memory. VMware 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 256 MHz. VMware HA Slot is the default admission control option prior to vSphere 6.5. Slot Size is defined as the memory and CPU resources that satisfy the reservation requirements for any powered-on virtual machines in the HA cluster.This article is just to cover how the HA slots are calculated step by step not more than that.
By Duncan Epping, Principal Architect.
Vmware Fixed Slot Size
Vmware Cluster Slot Size Calculation
On the VMTN forum today someone asked how it was possible that the “used slots” exceeded the “total slots”. This is what their environment showed in vCenter:
HA Advanced Runtime Info:
Slot size 4000Mhz
4 vCPUs,
4232MB
Total Slots in Cluster 16
Used Slots 66
Available Slots 0
Total Powered on vms in Cluster 66
Total Hosts in cluster 2
Total good host 2
You can imagine this person was very surprised to see this. How can you have 66 slots used and only 16 total slots available in your cluster? There are two possible explanations:
- Admission Control is disabled
- A reservation was set on a virtual machine after all virtual machines were powered on, skewing the numbers
Let’s tackle number 1 first. If you disable admission control the vSphere UI will still show the slot size and the number of slots etc, it just won’t do anything with it…
With regards to the second explanation it might be easier to give an example:
Vmware Ha Slot Size Calculation
Just imagine you have 2 hosts and HA does its calculations and you have 100 slots available. You power-on 100 VMs. Now you set a reservation on a VM, this reservation will change the slotsize. HA does it calculations again based on this new slotsize. This will result in only 25 slots available based on this new slotsize. However you already used 100 slots. In other words, now you have 25 totals slots and your used is 100.