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From Sanjeev Neelarapu <>
Subject RE: FW: Regarding the vm.allocation.algorithm.
Date Thu, 11 Jul 2013 11:29:36 GMT
Thanks Prasanna. I was trying to understand the impact of these global setting parameters on
the dedicated resources feature.

-----Original Message-----
From: Prasanna Santhanam [] 
Sent: Thursday, July 11, 2013 4:40 PM
Subject: Re: FW: Regarding the vm.allocation.algorithm.

This is how the planners determine where to place the VM based on needs like enough capacity(cpu,
memory, storage)

Once the available capacity and requested capacity is determined, the following heuristics
are applied to determine the final deployment plan of the VM:

1. random will choose a random host for the VM (note: random doesn't imply it won't go to
the same host. that may appear as an aberration)

2. firstfit as the name suggests will put the VM in the first suitable host that is available
with enough capacity

3. userdispersing - choose the cluster such that other VMs of the user
(account) are placed as far apart as possible. As far apart being different clusters - different

4. and 5. are related - concentration basically is the inverse of dispersion. try and put
the VM as packed and close as possible wrt other VMs of the user(account). So VM1 and VM2
are said to be concentrated if they belong to the same pod.

The need for 3 arose from providing basic tolerance to failures in physical resources. And
the need for 4. and 5. arose so as to provide better performance (read, write, network) to
VMs in a group.

Apart from all this there are affinity/anti-affinity groups. Host and Storage tags, HA dedicated
hosts, HA tags, etc that can determine the placement/planning of VMs.

Under what context are you looking to understand this though? That can help explain the algorithms
involved further.


On Thu, Jul 11, 2013 at 09:44:24AM +0000, Sanjeev Neelarapu wrote:
> From: Kiran Koneti
> Sent: Thursday, July 11, 2013 3:13 PM
> To: #Cloud - Engineering
> Subject: Regarding the vm.allocation.algorithm.
> Hi All,
> Where can we find the documentation for the "vm.allocation.algorithm" global setting
> I just wanted to know the behavior of the different values for this parameter. I see
the below values but want to know what is the functionality of each.
> 1)random
> 2)firstfit
> 3)userdispersing
> 4)userconcentratedpod_firstfit
> 5)userconcentratedpod_random
> Regards,
> Kiran.

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