Hi all,

Just looking into ideas for now but would love to hear/ read experiences of other users. So as the title reads:

How many VMs are you running simultaneously and how responsive are they?

Do you allocate the same RAM for each machine or have them specifically configured uniquely?

Do you leave the Host with more RAM for all the workload or just the bare minimum?

Do you find yourself in the VMs more than the Host?

What kind of CPU are you using and are you satisfied with the performance?

Any and all feedback is welcome.

errr... really? no starting conditions? I am running about 80000 VMs right now, they are all responsive and happily puffing away.

Whoa! I guess I didn't realize the computing power of some.

Could you clarify on the starting conditions? Is this one Host or many?

of course it's many hosts, many datacenters in fact. This is why I ask, you have a very YMMV-ish question, with no actual background described.

Well I meant on any single Host, how many are running efficiently?

it highly depends on the hardware itself. Usually every VM need at least one core, but it also depends on the usage, what is installed.... (not to speak about nested VMs)

I run between one and four... But I also have a dual quad core Xeon.

But since I only allocate one core per VM I expect some sluggishness - depending on what I'm doing. GUI testing is sucky, but general applications are reasonable for single core operation.

Is it safe for me to assume that for a consumer grade PC (AMD FX 8350 Vishera 8 core) it can run a max of 7 VMs? And 1 core left for the host...

Depends on what you are doing in addition to that "1".

If you have situations that need two or more active VMs, then another core for the host is more useful as they can handle the necessary memory scheduling and I/O support that may also be needed.

Specially when that host is also performing GUI control functions (one core ends up mostly handling the GUI).

That was why I try to limit myself to 4 VMs. That leaves one for GUI control, one for I/O and and another if necessary, and a spare if things get busy.

The usual problem with consumer grade PCs is that they have really crappy I/O capability. And that causes a lot of contention. The only way it can be reduced is by using more host memory for buffers... which limits the VMs memory use.

on a typical 2 socket pizzabox, you could run up to a few hundred VMs, it all depends on what these VMs do and how they are configured. As long as you don't overcommit the CPU on any single VM, you can go very far with (mostly) idle machines.

For typical office worked VDI, for example, the standard calculation is 1:10 (i.e. 10 desktop VMs for every physical core, HT not counted of course)

That 10 to 1 assumes efficient I/O which does not exist in a pizzabox. And you can't run a few hundred VMs in even an 8GB workstation efficiently - it would be thrashing the disks to death.

The question is way too broad to answer. It all depends on the resources available on the host and what you want these VMs to do.

If you have a host with 128 GB of RAM and 20+ CPU cores and your VMs will be CLI-only providing basic command line services with minimal load (git server, svn server, dns server, etc.) then you can run hundreds at the same time without issue.

If you have a host with 4 GB of RAM and 2 cores and you want to run a Windows 7 VM to play games - you probably won't even be able to run that one effectively.

It depends on the expected load on those VMs and what you want the host to be able to do while they're running. Assigning a core to the VM does not remove it from the host, it's more of a CPU usage cap on the VM. There's no reason you couldn't have 20 VMs with 1 core each on an 8 core machine, as long as all of them don't fire up and try to saturate their CPU at the exact same time. RAM is usually the limitation, not CPU, unless you're running some very CPU-intensive VMs.

A typical VDI workload for up to 100 desktop VMs, doing office work (MS office, web browsing etc) does not generate enough IOPS to overwhelm a locally accessible (6Gbps SAS) 6 disk raid10. Yes, there are pizzaboxes with 6-8 disk slots easily available from most server vendors. Should I add SSD or FusionIO into consideration as well?

I've not even seen advertised a pizzabox with enough room for 6 to 8 disks... That usually requires a 2U (to 4U) slot server...

And note - you said SERVER, not PC. PC workstations tend not to have SAS in the first place.