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naveenvm
Enthusiast
Enthusiast

Resource allocation - Cluster with Resource Pool

I was blank when one of my collegue asked me this. Would like you all to please give me your inputs too. I have worked many a times on clusters and resource pools and as I know............Clusters are a way to make a grouping of all resource of N no. of ESX machines and Resource pools are used to hierarchically partition available CPU and memory resources.

But I think(may be wrong), that both these are logical boundaries and are not physically taking control of the resources (CPU and memory). In the end the VMs are gonna run on the physical ESX box only and taking resources from it directly.

Consider a case where I am having 2 ESX box with config. as (2 CPU cores and 2 GB memory) = 4CPU, 4GB RAM Total. I created a cluster of these 2 ESXs and within it created a resource pool with 4CPU and 4 GB memory. Now I am running only one VM inside this with 4 CPUs and 4 GB memory and consider it is utilising nearly whole of them. Now with the concept of clusters that we have, do we mean that this VM will run with resources of both ESX servers simultaneously (if yes, HOW) , or it will just pretend to be running on this cluster but will ultimately run on a single ESX server with, say overcommitment ???????

NUTZ

VCP 3.5

(Preparing for VCP 4)

NUTZ VCP 3.5 (Preparing for VCP 4)
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conyards
Expert
Expert

"Consider a case where I am having 2 ESX box with config. as (2 CPU

cores and 2 GB memory) = 4CPU, 4GB RAM Total. I created a cluster of

these 2 ESXs and within it created a resource pool with 4CPU and 4 GB

memory. Now I am running only one VM inside this with 4 CPUs and 4 GB

memory and consider it is utilising nearly whole of them. Now with the

concept of clusters that we have, do we mean that this VM will run with

resources of both ESX servers simultaneously (if yes, HOW) , or it will

just pretend to be running on this cluster but will ultimately run on a

single ESX server with, say overcommitment ?"

The VM will not run with resources across two hypervisors, that is not possible. In fact you would not be able to create a 4 vCPU VM on an ESX host that only has 2 cores available to it. Now remember the key here is cores not CPUs, 1virtual CPU = 1physical CPU core. The maximum size VM in the example you have given above would be with 2vCPUs.

Simon

https://virtual-simon.co.uk/
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naveenvm
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Enthusiast

OK......forget about physical CPUs.............I am talking about 2 processor( 2 cores) ESX box.

In fact you would not be able to create a 4 vCPU VM on an ESX host that only has 2 cores available to it.

-I guess with ESX 3.5 we can allocate more vCPUs to the VMs, than CPUs available in the ESX. Done this many a times, so, this should be possible...!!!????

The VM will not run with resources across two hypervisors, that is not possible.

-Yes, this is what I expected too. But if this is the case, then what is use of clusters and their aggregation of resources, just for viewing purpose???? Ultimately resources will be used per ESX basis. I mean this statement doesn't hold any significance then –

A cluster is a group of loosely connected computers that work together, so that, from the point of view of aggregating resources such as CPU processing capability and memory, they can be viewed as though they are a single computer.VMware clusters let you aggregate the various hardware resources of individual ESX Server hosts but manage the resources as if they resided on a single host. When you power on a virtual machine, it can be given resources from anywhere in the cluster, rather than be tied to a specific ESX Server host.

Request you to please keep benefits of clusters i.e. HA & DRS aside, from resource aggregation/ allocation point of view we are not getting any benefit of clusters then ???

NUTZ

VCP 3.5

(Preparing for VCP 4)

NUTZ VCP 3.5 (Preparing for VCP 4)
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conyards
Expert
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You are managing the Cluster as a single entity, this is the advantage, what you cannot do is grow a VM to bigger than the component parts of that cluster. The advantages are fundementally HA/DRS etc...

I think yet again in your response you are confusing Physical CPUs with Cores.

If you have a server with one Physical dual core processor within, then you will have you will be able to create a 2vCPU Virtual machine, and as many of those as you want to (the hypervisor will do it's job and schedule them accordingly). What you cannot do is create a 4 vCPU server as you will not have enough cores available to process the VMs requests to the hypervisor, (I'm ignoring hyper threading for the purposes of the last sentence).

https://virtual-simon.co.uk/
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