Marathon makes a bunch of cool software for physical and virtual servers. One of their product lines offers High Availability (HA) for virtual servers called everRun VM. everRun VM comes in 3 flavors and one of those flavors (basic failover) is now built in to Citrix XenServer 4.2 - for free. Here are the different levels of everRun VM:

Basic Failover/HA (will be included in XenServer 4.2)

• Heartbeat between hosts
• Restarts VMs on different host in the event of a failure
• Non-critical IT Infrastructure where some downtime is acceptable

Steve Huisman gives a good overview of the other levels of everRun VM at virtualfuture.info.

“Level 2: component-level fault tolerance (available now) Creates a virtual machine on top of 2 other virtual machines. The Marathon-VM runs on 1 virtual machine and synchronizes IO to the other virtual machine. If, for example, the disk fails in one virtual machine, the disk in the other virtual machine will take over.

Level 3: System-level tolerance (available Q4 2008) Protects VMs against any type of failure and maintains the applications and memory in their pre-failure state.”

One of the really cool things about this technology is that it enables fault tolerance between geographically disperse locations. So, VMs can fail over to DR centers “automagically”.

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