Hyper-V - resources allocation

ELGowen
ELGowen used Ask the Experts™
on
HYPER-V Host capactiy - VM capacity (Windows Server 2012)

I have a Host Server with 16 Cores- 32 processors, 128GB Memory and 1TB Storage.  

I have a request for a new VM to be created on this server with the exact same spec as the host has.  There will be only 1 vm on this server.

Realistically what is the most that I can allocate to the new vm, taking into account the requirements of the host server ie. cores, memory, checkpoint storage, harddrive etc.

Thank you
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Architect
Distinguished Expert 2018
Commented:
If you try to create VM with static memory equal to host memory, VM won't start

What you can do, create VM and before staring it, from VM properties\settings change static memory to dynamic and assign startup memory to something like 8 GB and keep minimum 8 GB and maximum unlimited (whatever shown on screen) which allows you to take as much as available memory on host for VM whenever required.

2012 hyper-v supports maximum 64 vcpus, you can assign maximum 32 cores which is your physical server have
Lee W, MVPTechnology and Business Process Advisor
Most Valuable Expert 2013
Commented:
VERY unwise to allocate all vCPU - even most vCPU.  If the only thing the host is running is that one VM, I MIGHT be willing to go to as much as 24 vCPU (since you have 32 vCPU available) but you'd be wise to start with fewer and go up SLOWLY and ONLY as CPU demands are clearly needed.  Why?  I'd suggest reading the article about how too many CPUs SLOWS DOWN VMs.

https://www.zdnet.com/article/virtual-cpus-the-overprovisioning-penalty-of-vcpu-to-pcpu-ratios/

(It may be old, but it's still applicable).

Author

Commented:
Thank you, what would you recommend with the memory, they have requested 128 GB of memory for the VM. Could the host server survive with 4gb of memory (giving 4gb to the host and 124gb to the vm) or to assign as Mahesh mentioned giving 8gb.
MaheshArchitect
Distinguished Expert 2018
Commented:
Unless we know your application prerequisites, its difficult to suggest exact memory requirement
If application cannot start without 128 gb memory, then you won't even built VM as you have 128 gb memory

If above is not the case dynamically assigned memory will work better and your host and guest both will survive, no need to static memory allocation
Tomorrow if your vm memory utilization increased more than 124 gb, u can add more physical memory to server

Author

Commented:
Thank you both for the advice

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