One of the goals for this project was to try out the fancy thing that VMware calls VMotion. Basicly it is a system where you can move virtual machines around between physical hosts without having to power them down. By enabling VMotion you create an opportunity for virtualized load balancing in virtual data centers which is quite cool :-)

The VMotion requires that you have your virtual machines on some kind of centralized storage, for example iSCSI or Fibre Channel. When you or the load balancers initiate the transfers, ESX takes a snapshot of RAM content, moves it to the new hosts while concurrently logging changes from the log to the current state. When the RAM content are safely relocated to the new physical machine, the virtual machine are powered off and the change log are sent to the new host which are then powered on. This should appear as nothing have happened for the users outside the data center.

After setting up my lab, this was one of the first things I wanted to try out. After a quick install of Ubuntu on my new iSCSI disk, I initiated the migration. After some 20 seconds the virtual machine was on its new host and that without missing a single ping packet. I must say, I am quite impressed!

20 seconds is quite a difference from the usual work flow involved in moving systems from an old host to a new host before the world became virtualized. Either you had to move some disks around between the machines or you had to install both the operating system and the necessary applications on the new host before moving the data. Both methods gives you a significant amount of time where the service is unavailable, especially if you hit some kind of problems. Now, it is done with the push of four buttons without having to the take service down at all.

Needless to say, I just love it! :-)