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For a project I am trying to get real-life estimates for the number of virtual machines per server, both typically and maximally.

Of course, the maximum number of VMs would be depending on the type of applications (disk intensive, network intensive, ...), and server hardware (like number of cores, memory, ...), but still it would be useful to know if a typical maximum is about 10, 20 or 30 VMs per server.

Can anybody give practical numbers?

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Please mark your question as community wiki since there's no correct answer. – ThatGraemeGuy Oct 29 '10 at 8:45
@graeme: I don't have enough karma to do so... – Rabarberski Nov 3 '10 at 8:41
up vote 5 down vote accepted

There are none - the main problem is that servers GREATLY vary. LAst days here some people posted their virtualization servers with 12g RAM. My smallest ones have 16, my main ones 64. This OBVIOUSLY impacts the number of machines I can run on them.

In general, given higher end hardwar (server level - mostly to have the RAM) 6-10 or so virtual cores per physical core seem to be a nice number. But this is a VERY wide area. I have some VMs that are RAM heavy (running databases) and one day may require their own server nearly. I have others that live in 368mb RAM do do nearly nothing (mostly DNS server etc.). SO, while you can have a middle ground, the variation is very wide.

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you cannot estimate how mny vms per host can get if you don´t know the performance required per vm. Because Vmware use a algoritms that give to the virtul machine the resources that nee in determinate time. by example if you asign 12gb of memory and 4vcpu. and in the real world this machin use a 5gb of memory and 750 mhz. of CPU Vmware only give to the virtual machin only resources that need. however if no limits in cpu and shares and memory.. and the virtual machine need more that you asign vmware overcommit resources for this vm.. the best practice in this case is moniting the enviroment before consolidation poces and use tools as platspin or vmware capacity planning objects for get all you can need in resources as network, memory, cpu, iops for every server that you need virtualize.

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There's not nearly enough information. Is this server a C64, or a Cray ? How many cores ? How much ram ? What load ? Are they idle ? What networking ?

I'd say a reasonable esitmate would be 0 to a million.

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VMWare's vSphere/ESX/ESXi let you have up to 320 guests per host.

That said it depends as you say on the load, I have many hosts with 3-5 guest on but then for development/play hosts I've seen 70-80 before now.

Personally I wouldn't want to run more than about 12-20 vaguely busy production guests per host but that's me.

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To add to the above suggestions, with an exact idea of what Hardware (no. of processors and amount of ram) you can divide it amongst your Virtual machines, leaving some for the HOST too.

Maximum are 384 VMs, have a look at the links above will give you good insight into it.


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The technology used can matter a lot:

Here you have 1000 lightweight virtual machines (Solaris zones) running on a single 64GB server:

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