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On a virtual machine, if cat /proc/cpuinfo tells me that there are 4 CPUs, is this just as meaningful as if it were bare metal? Should I configure my server (for example, # of Nginx or Apache workers) the same way I would on a bare metal server?

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2 Answers 2

It very much depends on the virtualisation solution being used. If you have multiple CPUs showing in VMWare then you have multiple vCPUs assigned to your VM in which case it is probably best to arrange your server processes in a similar way that you would a pair of real cores (with the caveat that due to the way vCPUs and real cores are scheduled sometimes you are better off not giving VMs more than one vCPU via VMWare if you have a relatively heavily loaded host. Other similar solutions probably work the same way, but some (especially those that are really partitioning one kernel rather than providing VMs often report the host's full capabilities even though your partition is, for example, effectively locked to one core.

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How can I figure out the virtualization solution being used? –  John Bachir Sep 10 '10 at 20:06
    
It will usually be documented on your hosts website and the emails you got on sign-up. If not there are usually clues in the /proc/ filesystem, but finding the information stated by your host is probably easier and more accurate than /rpcoi forensics. Common hypervisor names to look for (in no particular order): KVM, Xen, VMWare, VirtualBox/VBox, OpenVZ, Hyper-V, Virtuoso. –  David Spillett Sep 11 '10 at 12:02

It depends on the Hypervisor. If the Hypervisor is simluating 4 processors in 1 thread on the physical processor then your VM is better off treating it like 1 CPU. If the Hypervisor is passing through 4 physical cores to your VM, then you're best off using them.

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How can I figure out how it's implemented? This is on a linux VM on a popular provider. –  John Bachir Sep 10 '10 at 20:06
    
Tell us which provider, and we can probably tell you. Most likely it is Xen, unless the site specifically advertises itself as a VMware vCloud provider. –  rmalayter Sep 10 '10 at 20:30
    
Rackspace cloud –  John Bachir Sep 10 '10 at 20:38

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