title: Running many virtual machines on a single host
body: <p>I have a need to run a relatively large number of virtual machines on a relatively small number of physical hosts. Each virtual machine isn't doing to much - each only needs to run essentially one basic network service - think SMTP or the like. Furthermore, the load on each is going to be extremely light. </p>
  
  <p>Unfortunately, the numbers are something like 100 virtual machines on 5 physical hosts. Each host is decent enough - core 2 with 2 gigs of ram and a 1tb disk. However, I know just taking a vmware image of ubuntu and throwing on that machine wont get me anywhere near 100 instances and would be something closer to 20.</p>
  
  <p>So, is there any hope for this ratio of images to hosts? Also, which implementation of virtual machine would be best suited for this purpose - ie has efficient overall usage of resources? We mostly use vmware here, but if there is a significant performance advantage that could be gained by switching to Xen or the like, I am sure we would consider it.</p>
  
  <p>Thank you in advance for your insights :)</p>
  
  <p>Note: We ended up using OpenVZ and it worked rather well. The default parameters for an ubuntu template let us run about 40 instances per machine.</p>