Low Cost High Availability Solutions

We recommend KVM virtualization for most systems in our data center, including Windows systems, because of its inherent flexibility.

One of the solutions available as a result of KVM (or Xen) is the Ganeti high availability solution. Ganeti is a cluster management solution. Ganeti lets you replace Raided media with raided virtual systems. From a hardware perspective, this lets you use a single SSD or a set of striped SSDs on each machine, avoiding the need for a Raid-10 or Raid-5 solution with expensive flash. Instead, you simply install the virtual on a second machine and real-time update it using the Ganeti tools. You can swap between virtuals with just a few seconds of transparent interruption - long enough for Ganeti to copy the memory contents from one system to another. And if the first system fails, you can immediately boot the Ganeti enabled mirror. If you have a lot of similar virtuals, mirroring does not need to be done system to system. For instance, if you have 32 virtuals and operate on 4 different boxes, you can instead use five boxes, distributing the individual backup virtuals among the other four systems. In such a round robin topology, the Ganeti approach can actually cost less than four boxes with Raided media.

Ganeti is a good local solution. Because the remote system needs to acknowledge write IO before it is flagged as committed, this solution does not work well over long distances unless one uses triple redundancy and has high speed access only available in a data center.