Lamont Peterson on XEN and Virtualization


Lamont Peterson, co-founder of NeverBlock is talking about XEN and virtualization.

The talk is an intro to virtualization technology and a discussion of why use virtualization. Here are some pros:

  • Resource consolidation: fewer systems to buy, own, manage, power, cool, etc.
  • Unification: all VMs have the same "hardware" even if they're running on different hardware.
  • Access and management tools allow VMs to be managed over the network.
  • Utilization: most bare metal systems are under utilized. VMs allow that resource to be recovered.
  • Fewer physical machines can improve reliability since there's less

Of course, there are some cons:

  • It can be more complicated to set up.
  • Administrators have another layer to learn and work with.
  • Physical servers need lots of RAM.

It's a good idea to keep some headroom on each machine so that VMs can be migrated when a physical box dies. This gets easier (and less costly) as the number of physical boxes you're using grows. Here's my analysis: The headroom you need is somewhat greater (20%) than 1/N where N is the number of servers. So with 2 boxes, you can use about 40% of each machine and still be able to migrate everything from one machine to the other in the case of problems. With 10 boxes, you can load boxes up to 80% (as much as I'd do in any event) and still have room to migrate a single bad server's VMs. XEN supports live migration if you get the storage architecture right.