How many virtual machines could be run on top of a physical host machine at the same time?

Question

I have been facing problem with my host machine having 4GB RAM and Intel Core i3 (2GHz) processor. I am trying to make a cluster with few virtual machines (VMs). Anyway, It is just fine with 2 VMs having 1GB RAM each. The system is just out of control when the number of VMs is more than 2 and hence it is required to force reboot so that it is operable again.

Questions:

• Is the any general rules for running the maximum number of VMs at the same time (depending on the RAM, CPU etc)?
• Can a virtual memory or a swap memory (at the host machine) is helpful to overcome this problem?

Update:

I re-create same VMs on my lab where the RAM were 32GB (8GB usable) with intel core i5. This is not also very much helpful and I am facing same problem.

Again, I tried to make these VMs on some other computer with 63GB (8GB usable) RAM. This time it is also happening somethings.

From these setup, I got my 2nd question that I asked here.

Solution 1

A 64-bit machine needs about 4 GB (a bit less) to run effectively. You can run one VM effectively in that.

I have a Windows 10 Host with VMware workstation and 16GB of memory. I can run about 4 Virtual Machines comfortably each with 1.5 to 2.5GB of ram. Virtual Machines need memory too.

8GB would work for a couple of normal machines and may a third small one if 8GB is your maximum memory.

Also remember that an i3 is not a strong CPU so in many ways the machine you have is not made for 64-bit Virtual Machines which is very common now. I hope this added comment is helpful

The above setup (my machine allows me to run everything I do run effectively and without lag.

Solution 2

This is an extremely broad question so any answers will also be extremely broad as will this one. The answer is that it depends. You can run as many or as few as your computer can reasonably handle. This depends on the operating system of the VM you are running as well as the amount of resources you allocate to a particular VM.

Of course, the resources you allocate should not exceed physical specifications of your computer. It is possible to do this, however this would be know as overprovisioning and can lead to poor performance.

Ex. Ubuntu server will consume far fewer resources than a Windows 10 VM because it does not include a GUI. As such, you can run many more Ubuntu server VMs than you can Windows 10 VMs.

There are numerous additional factors that can impact performance as well. This can also include items such as the host operating system, for example.

Comments

[Ramhound]

You need to specify how much memory each VM will be given.

[testuser]

@Ramhound... each VM have just 1GB RAM.

[John]

1 GB of memory is small and will lead to paging in memory

[Ramhound]

@testuser - Each VM would consume 1 GB, plus any other applications you have installed, with only 4 GB it’s not wonder you see performance after spinning up another VM

[CaldeiraG]

8GB of ram is still very low and 1GB per machine will lead into stuttering issues. Consider using more RAM per VM.

[testuser]

@Ramhound yes, make sense.