First one I checked on supermicro's site:
http://www.supermicro.com/products/s...8U-TN10RT_.cfm

1U with 10x 2.5" NVMe hot-swap bays. That's a hell of a lot of I/O capacity there.

Yes, I use servers to run my virtual machines. Do you think I'd be using desktops for production deployments?

As for pizzaboxes, those are typically 1U boxes, and yes, there are 8 2.5" backplane servers available, moreover, since CD drives are not really needed any longer, 6-8 disks is pretty much the industry standard.

I just checked, Dell R630, which is their standard 1U machine, not budget friendly, but also not the top of the line, also comes with 10 a disk backplane. In fact, you can probably find 6x 3.5" backplanes available as well. And remember, there are new disk form factors coming up, especially for SSDs, which means in a couple of years, you'll see at least 20 2.5" SSDs in a 1U machine. Beef that up with 24 core CPUs, and 100 VMs per 1U is an underachievement really.

The original poster was talking about desktop PCs. Not servers.

not in the original post he wasn't. He did not mention a single detail about the hardware he had in mind.

Well this topic got fired up huh! Thanks guys for the feedback I just was looking for a little insight about Virtualization as a whole. No originally I didn't specify the type of hardware and I apologize for the vagueness of this topic.

Thanks @dyasny, and @jpollard you guys are great.

Anybody else feel free to just share your experiences as well. I like viewing what is going on in the computer world as a whole because it allows me to think outside the box.

Currently the most I have put to use is a mere 2 but that will soon change. Thanks again.

What , you all did not save ur old cases ? , and excess hard ware ?
My hardware
Gateway 2000 case with 4 front spaces [2 are for DVD multi play & record]
inside , scavenged hard point for 2 stacked [X2] to hold 4 altogether
2 still using all IDE [98SE & UBUNTU], 1 mixed [XP & Ubuntu[, 1 EIDE [Ubuntu],
[friend has SCSI [ 5 HD ] with 1 Blue ray EIDE [NT & XP & [Ubuntu so i can erase viruses ]]
[ we build our own ! ][just can't get him into Linux yet, but its there for him if needed !]

You can run many VMs if they are mostly idle. I have a setup on a 4-5 years old mini-laptop with 6GB of memory (HP Probook 5220), 3 to 5 VMs running an OpenStack cloud. That is, there are VMs running inside those VMs. Slow but usable. Not for production though

Don't think that a CPU core needs to be dedicated to a VM. If you have two or four cores or hyperthreads, you are not limited to two or four VMs. The most limiting factor is probably not CPU but memory.

I run 3 VM's on my host computer. but I am using VMWare.

I assign 4 gig to my windows, and 1 gig to my others. . (mostly ubuntu).
My host has approx 8 gig of memory.

Where my speed really hurts, is switching between the VM's. . but once on the VM, it is "ok". . slow at some spots, but Ok in running.
In my windows VM, I run a huge compiler. . .heavy on resources. Thus 4 gig of memory.

One guest system I use for surfing. . .Just in case a virus decides to come in, it is isolated to that once guest system.
Then I run a server and testing platform.

How about some mainframe figures for a change ?
The hypervisor in a mainframe (IBM z) is z/VM.
RedHat and SLES has been supported this s390x architecture since about 2001. Ubuntu will do in 2016.
Since the knowledge of mainframe related stuff is low outside the mainframe community, I thought you might be interested in some hardware facts.
Actually it's very much in use. Just one example: (CICS is a mainframe Online transaction system)
On this Planet per second there is about 30 000 Facebooks Likes, 60 000 Google searches and 1 160 000 CICS transactions.

And to your questions, answer is for one physical z/VM instance (which in fact runs in an so called LPAR in a mainframebox):

How many VMs are you running simultaneously and how responsive are they?
About 120 system about half running critical production load, very responsive.
Fun fact: If you have a Linux only fully loaded mainframe box of latest model you need 4 z/VM systems that will run a total of about 8000 Linux servers.

Do you allocate the same RAM for each machine or have them specifically configured uniquely?
Each machine separately configured. They have one startvalue and one maxvalue.
For example starts with 4GB and MAX=16GB. You can activate more memory on the fly up to defined max limit.
If you want higher max value, change the max definition and reboot.

Do you leave the Host with more RAM for all the workload or just the bare minimum?
Just a little more than it needs, we don't want it to swap, z/VM does that job much better.

Do you find yourself in the VMs more than the Host?
Mostly in the hosts, but not that most :-)
Depends on what tasks you currently is doing.

What kind of CPU are you using and are you satisfied with the performance?
It's an mainframe architecture z CPU (one core per CPU) running at 5.5 GHz.
We run in average 30 Linux servers per CPU.
Our Linux servers shares all cpus, and all other resources including 200GB memory.
Yes, happy with performance. It's mostly a tuning thing, but if hitting the limits:
We can add more memory or CPUs on the fly.

Thanks for your feedback DaTore that was some interesting information.