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VMWare CPU Reservation

Posted on 2014-08-01
Medium Priority
Last Modified: 2014-08-01
I have a vm that the supplier is requesting CPU reservation on, i know CPU reservation works differently to Memory reservation so the CPU is never entirely reserved for the VM but they cant be swayed.

As this isnt something i have done before my query concerns multicores on the VM and how much i should be reserving?

the  VCPU i assigned is a single socket quad core which shows in windows as 2.3GHz so if i am to reserve this on the VM do i reserve the 2300 MHz or do i need to reserve 4 x 2300 MHz (one for each core)?
Question by:LHT_ST
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LVL 124
ID: 40233799
If you want to ensure, that the VM, always gets 2300MHz cycles of CPU, reserve at this amount.

Are you running many VMs on this hypervisor, because Reservations are often only required, when a host is over subscribed.

How have you setup the number of vCPUs for this VM, and you are better just allocating sockets, rather than cores. (unless for licensing reasons).

performance is the same.

Reserve what cycles you require, so if you have 4 x vCPU at 2.3GHz, reserve


Author Comment

ID: 40233800
none of the links provided actually answers the question - i have already provisioned the CPU and am aware of how vmware manages the CPU resources (Shares etc) but i need to know if i should be reserving 2.3 GHz total or 2.3 GHZ per core for vCPU?
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Author Comment

ID: 40233804
Andrew, Yes this is oversubscribed but unfortunately our customer is in the habit of taking risks with the infrastructure they own.  As i stated originally i have tried to sway the supplier away from CPU reservation but they want it to be completed.

Thanks for any assistance
LVL 124

Accepted Solution

Andrew Hancock (VMware vExpert / EE MVE^2) earned 2000 total points
ID: 40233805
I think we just cross posted...

Reserve the cycles you require, so if you have 4 x vCPU at 2.3GHz, reserve


Reserve = Guarantee, so you will ALWAYS Guarantee 9200 for this VM.

Author Closing Comment

ID: 40233809
Thanks :)
LVL 124
ID: 40233818
A word of caution, Setting Reservations can have a "Domino effect"

e.g, you fixed 9200 of CPU resource to 1 single VM, which will then take away 9200 from the total CPU pool always, even though the VM may never request 9200, it's always there just in case it needs it.

This can cause other VMs to struggle, when you then need to start setting CPU reservations on other VMs, and eventually, you've got none left to reserve!

So.....9200 cycles, is assigning all the cycles in the host processor to the VM, but you may want to check, how many does it really need.

Usage versus Defined maybe very different.

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