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buzzlightyear_2
Contributor
Contributor

Understanding percentage based admission control


Hi all,

So I thought I understood the admission control policy but clearly not, can someone please help me understand why the below configuration is erroring with insufficient resources available when replicating a host failure.

I have the following setup

2 x v5.5 ESXi Hosts each with 16GB memory and 12 x 2.493GHz CPU's (29.9 GHz)

4 x win2008 machines with 1 vCPU and 2048MB memory each, no reservations have been set.

I'm using percentage based admission control policy and I have it set to 10% for both CPU and memory.

So

Total memory = 32GB

Total CPU = 59GHz

4 x 2008 servers totaling 4 vcpu & 8192MB memory (no reservations)

admission control set at 10 % for both cpu and memory

If i place one of the hosts into maintenance mode i get the error insufficient resources available, please help me understand why?

From my understanding.

Percentage based policy works off reservations set and because i have no reservation on any of the VM's only overhead is considered, therefore I believe the percentage is calculated using the following

(Memory reservation + memory overhead)

Default CPU which is 32MHz

I've calculated it as,

Memory = (32 - (VM1 = 0+100) + (VM2 = 0+100) + (VM3 = 0+100) + (VM4 = 0+100)) / 32 * 100 = 98% - 10% = 88% available after deducing 10% allocated to admission control.

CPU = (59 - (VM1 = 32) + (VM2 = 32) + (VM3 = 32) + (VM4 = 32)) / 59 * 100 = 99% - 10% = 89% available after deducing 10% allocated to admission control.

Thanks

1 Reply
depping
Leadership
Leadership

Why? Well if you have 2 hosts, and you place 1 in to maintenance mode... there is not much HA can do when it comes to restarting virtual machines?! In other words: you have just 1 host left, if that one goes dead then there is no spare capacity. Hence you are getting this error message Smiley Happy