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Resource pool , VM running in ESXI server

Posted on 2014-09-23
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Last Modified: 2014-09-24
Hello Experts,

I have a question below questions about resource pools which is feature of VMWare Hypervisior.

1). A VM running in a ESXi server , how it uses the resource pool allocation? I mean , we might have VM which in a single ESXi host which ,might be spaned across the different resource pools. How hypervisior identifies VMs and their associated Resource pools?

2).In case of resource contention how much of resources will be assigned to the VM? I know , it all depends on the Shares what we have for a resource pool? but Question is how much of resource will be assigned to the VM from the ESXi host where it is running? Is there any calculation?

3). Is it worth using Resource pool? I dont think find any reason to use it. As we already have some vSWAP , Ballooning etc already built in the hypervisior. Can someone give me a good reason why we require it? :)

Thanks,

-Prashant Girennavar.
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Question by:Prashant Girennavar
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by:asavener
ID: 40339919
First, you have to understand that resource pools only kick in when there is contention.  Basically, it's a way of making sure that your high-importance workloads aren't impacted by low-importance workloads.

Maybe you have Production machines and Development machines on the same cluster.  If one of the Dev boxes suddenly tries to grab all of the CPU, your resource pool configuration can prevent that runaway machine from affecting the workloads you specify as high-importance.

You would not configure a single resource pool.  You would configure at least two resource pools, and place your VMs in those pools.

There are calculators for resource pools.  You should be able to google them.

The use case for a resource pool is to avoid the use of reservations.  Since a reservation prevents other workloads from using the reserved resources, it's literally a denial of service.
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by:asavener
ID: 40339934
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by:Prashant Girennavar
ID: 40340858
ok.

I understand,

So, Last question , incase of resource contention , from where these resource pool pull the resources????

Is it from individual hosts? or from cluster?

Thanks,

-Prashant Girennavar.
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by:asavener
ID: 40341491
It depends on where the resource pool is created, but typically it's applied at the cluster level.  Each host is a resource, and the cluster is a big pool of resources.
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by:Prashant Girennavar
ID: 40341574
ok

Say it has been created on cluster level, so , at the time to resource contention , Resource pool make use of all the 3ESXi host Physical CPU???

  I have always heard , VM run into the ESXi host not on cluster level.


Thanks,

-Prashant Girennavar.
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asavener earned 500 total points
ID: 40341938
Yes, contention happens between guests on the same host.

When contention happens, the ESXi host compares the share values assigned to each guest, and allocates resources based on the shares inherited from the resource pool.

So if you have 30 VMs, each VM inherits a share value based on the resource pool.  When there is contention, the host sums up the share values of the local guests, and then assigns resources proportionate to the guests' shares.

It is possible that all guests on a host will belong to the same resource pool, but it is unlikely if you have a reasonable number of VMs.
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by:Prashant Girennavar
ID: 40343316
This is exactly what I was looking for.

Thanks for the explaination.

-Prashant Girennavar.
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