Maximum CPU and RAM to virtual Image

[mithrandirr]

Hi All,

I have host machine with hardware configuration 2 cpu each with 4 core i.e. total 8 core and 16 GB Ram. On this server single Linux image is running, which has mysql in it. currently image is using 4 cpu core and 4 GB RAM.

As I am observing some performance issue, I wants to increase cpu and RAM allocated to virtual machine.

Can anybody will let me know maximum CPU and RAM I can assign to image without destabilizing or getting any error.

I am running VMware ESXi 5.5.0

[Alistar]

Hello,

if you are running a single virtual machine on your hardware, you can manipulate its resources to your liking without worrying that you would choke other VMs running there. General guidelines are:

• CPU - ESXi scheduler likes to utilize n amount of sockets per 1 core. So say you'd like to bump your VM to 6vCPUs, you'd set 6 virtual sockets with 1 core per socket & modify the VM's Configuration Parameter numa.vcpu.min to 4. This will tell the ESXi host to present the NUMA topology to any system with more than, but not including 4 cores. This will give you the best performance you can get. If the previous would be too much hassle for you or you wouldn't feel comfortable, modify the VM to fit the underlying physical architecture, so above 4 vCPUs you would use 2 sockets and up to 4 cores per socket.
• As with RAM, you should always leave some for the ESXi host in order to prevent swapping, refer to my blog post here: In short, you should leave 2649MB Free for the ESXi host, so you should provision it with maximally 13735 MB of memory.

Any further questions you have, don't hesitate to ask :smileyhappy:

[mithrandirr]

Hi Alister,

Thanks for Information.

My doubt for RAM is now cleared but as I am new to VMware I still has some doubt about CPU.

1. I have 2 cpu each with 4 core on host machine.  My linux Virtual machine is at this moment running on 4 cores.

Can I increase this cores to 6 for Virtual Machine and keep remaining 2 cores to host machine.

We are never going to run another VM on this host machine.

[Alistar]

Hi again mithrandirr,

you do not have to worry about the CPU allocation. The ESXi's VMkernel is very flexible in terms of handling & scheduling the CPU resources. You would be fine allocating even the whole CPU horsepower you have (therefore 2 Sockets x 4 Cores Per Socket) to the server. The CPU cycles are run on-demand so you do not have to worry about making your physical host unresponsive or otherwise degraded in terms of performance. Therefore you can go ahead and increase the core count to 6 in either way I described above. Just for your information, the ESXi's internal processes (referred to as "worlds" ) always run on Logical CPU 0 and consume very few resources.

[mithrandirr]

Hi,

Today I checked the actual VMware image and it has 4 virtual socket and 1 core each configured.

As we wish to only increase core to 6 can I change CPU setting to 2 Virtual socket and 3 core each, will this work. Image running only support upto 8 cores.

[Alistar]

Hello,

yes this will work and is a desired vCPU configuration :smileyhappy:

[Nithy07cs055]

for server virtualization the conservative rule of thumb configuration is to use

number of vcups per core is 4-6, always follow the best practice from Vmware to have the better performance

also for memeory you can over limit , but always be ware of enabling the memory reclamation techniques TPS, ballooning, Memory compression and Host cache if available