Vmware HA , Slot concepts

[PrashantGirenna]

Hello,

I was reading host failures cluster tolerates , in Admission control and I was able not able understand below concepts.

Difference between Used and available slots

Difference between Available slots and failover slots.

I have below Advanced Runtime info in my Test VMware cluster ,

Here it shows , I have 89 Total slots,

Available slots = 0

Failover slots = 83

As Available slots = 0 , does it mean I wont be able to poweron the VM anymore if one of the host is going down? Please explian.

thanks,

-Prashant Girennavar.

[vThinkBeyondVM]

Did you go through this VMware Video on slots:vSphere HA Slot Size and Admission Control - YouTube?

There is one good blog post on the same: http://www.vmwarearena.com/2012/09/understanding-total-slots-used-slots.html

[PrashantGirenna]

i have gone through them before vikas,

They does not seems to explain what is available slot and what is failover slot.

If we have Available slot = 0 , does this mean we cant VM anymore? I just need to understand the terminologies given by vmware.

Thanks,

-Prashant Girennavar.

[vThinkBeyondVM]

Used slots:::. The number of slots assigned to powered-on virtual machines.

Available slots.:: The number of slots available to power on additional virtual machines in the cluster.

Failover slots.:: The total number of slots not counting the used slots or the available slots.

Yes, if available slot =0, it is mean that, as per admission control policy, you can not power on any other VMs

[PrashantGirenna]

Okay understood, Thanks Vikas,

So, if available slots = 0 , poweron of VM will not happen.

Now , why VMware has Failover slot in place? what is it significance ? where this will be used?

Thanks,

-Prashant Girennavar.

[Sateesh_vCloud]

Hey Prashant,

It is basically coming from Admission Control Policy of HA cluster. If you enable 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 N node HA cluster.So, It has to reserve some capacity for fail over purposes. 

Lets Come back to the Calculation

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

Available Slots  = (234 – 6)  - 78

Available Slots  = 150 Slots

[PrashantGirenna]

Thanks for your response, but question remains the same,

what is failover slot? will esxi use these slot? or it just a number.

Thanks,

-Prashant Girennavar.

[Sateesh_vCloud · Accepted solution]

Failover slots =  Slots reserved for fail over by admission control policy which are not used by ESXi