Vsphere Ha Slot Size Calculation

4/4/2022admin

This post is the follow up post for my previous post on VMware HA Slot Calculation. In that post, i have explained the step by step procedure for how to calculate the HA slot information. This post clarifies more on the Total Slots, Used Slots & Available slots in VMware HA Slot calculation. I strongly recommend to read my previous post on HA slot calculation to fully understand the concepts of this post.

Vmware Ha Slot Size Calculation
Vsphere Ha Slot Size Calculations
Vsphere Ha Slot Size Calculation Calculator

Used Slots = 6

Feb 05, 2013 The slot has two parts, the CPU component and the memory component. Each of them has its own calculation. If there are no virtual machine resource reservations in the cluster, then the slot size (for ESXi 5 at least) is 32 Mhz for CPU and 0 MBs + overhead for memory. (I’ve used 80 MBs as my memory overhead in the examples). Available slots = Total slot – Used slots i,e Available slots = 234 – 6 = 228. It should come as 228 as available slots but why Available slots is 150 in the above snapshot. Is that wrong or VMware did something wrong in HA slot calculation? Below is the method of calculation for Total Slots, Used Slots & Available slots. HA uses the highest CPU reservation of any given VM and the highest memory reservation of any given VM. If VM1 has 2GHZ and 1024GB reserved and VM2 has 1GHZ and 2048GB reserved the slot size for memory will be 2048MB+memory overhead and the slot size for CPU will be 2GHZ. Now how does HA calculate how many slots are available per host? The slot has two parts, the CPU component and the memory component. Each of them has its own calculation. If there are no virtual machine resource reservations in the cluster, then the slot size (for ESXi 5 at least) is 32 Mhz for CPU and 0 MBs + overhead for memory. (I’ve used 80 MBs as my memory overhead in the examples).

What is that? How does it calculate and our mind will think of the below calculation

Available slots = Total slot – Used slots i,e Available slots = 234 – 6 = 228. It should come as 228 as available slots but why Available slots is 150 in the above snapshot. Is that wrong or VMware did something wrong in HA slot calculation? Absolutely NOT. Below is the method of calculation for Total Slots, Used Slots & Available slots.

Available Slots = (Total Slots -Used Slots) – Slots reserved for failover capacity

How to Calculate Slots reserved for failover ?

It is basically coming from you Admission Control Policy of HA cluster. I have enabled admission control and configured Admission control Policy as ” Host Failures Cluster Tolerates” is equal to 1 . So It will make sure the resources always be available in the cluster as a reserved capacity to tolerate the 1 ESX host failure in my 3 node HA cluster.So, It has to reserve some capacity for fail over purposes.

Total Available Slots in the Cluster = 234

No of Hots in HA cluster = 3

Total Available slots per ESX host = 234 /3 = 78 Slots Per Host

“Host Failures Cluster Tolerates” Admission control Policy = 1 host Failure. So, 1 host failure should be tolerated in the cluster by reserving 78 Slots for fail over purposes.

Available Slots = (Total Slots -Used Slots) – Slots reserved for fail over by admission control policy

Vmware Ha Slot Size Calculation

Available Slots = (234 – 6) – 78

Available Slots = 150 Slots

Vsphere Ha Slot Size Calculations

I hope this post will clear doubts regarding Total Slots, Used Slots & Available slots in VMWare HA slot calculation.

Thanks For Reading!!!!

We recently moved our ISO store from a legacy NFS server to our main NFS filer.

The first task was copying the actual files, which can be done via any machine that has both datastores mounted (with read-write access to the destination store).

Vsphere Ha Slot Size Calculation Calculator

The more significant job is reconfiguring the VMs to use the copies of the ISOs in the new datastore.

Here’s the PowerCLI script I used:

It’s fairly self-explanatory.

The biggest caveat with this is that it assumes that the source and destination stores have the same structure, but it wouldn’t be difficult to amend it to change the destination path slightly.