Ganeti OSL Infrastructure

Ganeti is a cluster virtual machine management framework written primarily by Google. It offers us quite a bit of flexibility in scaling, deploying, and managing virtual machines. Instead of using ISCSI with a single point of failure like we currently use, Ganeti will utilize DRBD which is basically like having RAID1 (mirroring) over the network.

From a storage point of view, all the instances (virtual machines) will be using local storage on the server with a secondary node having its block device synced via DRBD over a private network. We should be able to handle N+1 failure with Ganeti (i.e. we can lose at least one node). There is currently no automatic way of failing instances over if a node goes down.

Instead of using Xen for virtualization, we’ll be using KVM, which will enable us to be 100% free and opensource with this environment. A major plus in our minds!

Reasons for choosing Ganeti

Our Xen cluster has been a great system overall the last several years, but lacks many important features:

  • Non-redundant storage backend
  • Lack of inexpensive scalability (requires expensive storage solutions for expansion)
  • Hardware doesn’t support VT/AMD-V so Xen is our only option
  • Xen Dom0 support is not included in the mainline kernel (hard to maintain)
  • Aging hardware
  • No cluster-wide management
  • No automated deployments

The recent outages with our backend iSCSI storage has pushed us to look at other options. Initially we were looking at using some type of libvirt based solution, however we discovered Ganeti and decided to give it a look. This was around the time that ganeti 2.0 was released and offered a large slate of changes and improvements including support for KVM. Here’s a list of the the important features and reasons we chose Ganeti.

  • Ease of node (Dom0) deployment and cluster expansion
  • Automated redundant storage (via DRBD)
  • Support for KVM (making it much easier to use newer kernels)
  • Cluster-wide management of VMs
  • Easy to use and unified tools
  • Deployment automation
  • Reporting and management tools
  • Useful API for writing automation scripts
  • Responsiveness of the Ganeti Community

With Ganeti, we can write better tools for adding new VMs, and balance loads on the nodes. It also gives us a cluster-wide view of our virtualization infrastructure and no longer need to log into each node to interact with the VMs. Since iSCSI is out of the picture, disk I/O should be much faster with the use of local disks. We can still run into the risk of I/O starvation but we should be able to limit it to one or two nodes. Additionally, it allows us to write tools that will enable our projects more direct access to the VMs for things like power cycling, console access, etc.

Check out the basics of how Ganeti works wiki page to have a better overall understanding of its framework.

Why not use Libvirt?

So why not use some type of libvirt based solution? Well there are several reasons, but the primary one being that its not a cluster-aware application. Each libvirt node works as a single host. While there are probably some projects out there that offer the cluster-wise solution, Ganeti is so much easier to manage with. Using ganeti does mean that we won’t be able to use already made tools such as virt-manager, however it will not take much time to build something that offers the same features. Ganeti replaces many of the things that libvirt does and puts it in a cluster mindset instead of a host-by-host mindset.

Infrastructure Overview

Here’s an overview of what our Xen and Ganeti infrastructures look like. We currently host around 60 virtual machines for various projects.

Xen Cluster Infrastructure

Hardware Summary

  • 3 Disk nodes (iSCSI) servers
  • 14 Xen nodes (Dom0)

Disk Node (Storage)

We use three servers running Gentoo Linux with the iSCSI ietd daemon. This is currently the single point of failure in our system and the cause of many of our recent problems with VM outages. They suffer from I/O starvation often if a VM ends up using a lot of disk I/O.

Xen nodes

We have 14 IBM HS20 blade servers with 4G of RAM that are getting close to 4-5 years old and run as the Dom0 for Xen. Each node has access to all of the iSCSI luns so that we can do live migrations. Doing migrations is done manually and is prone to errors sometimes.

Ganeti Infrastructure


  • 4 Ganeti Nodes (Dom0)

Instead of centralized storage accessed over iSCSI, each node (Dom0) in the cluster uses LVM on top of a redundant RAID configuration for instance storage. For further redundancy each instances disks are synced across two nodes. In case of a planned or emergency downtime we can simply move each instance to it’s secondary node where it can resume normal operation. This configuration gives us an easily managed and highly redundant storage environment while giving the projects we host faster and more reliable disks than were available on our Xen cluster.


We have 4 HP DL360’s with 24G of RAM and 730G of RAID5 storage available on each node and running Gentoo Linux. Each of these nodes have qemu-kvm installed and KVM enabled in the hardware and kernel. If we lose one node, we can still keep all of the VMs online after failing them over.

Once we run out of space in the current cluster, we can simply add another node and balance out the nodes with some tools. The node does not need to be exactly the same in specs, which gives us a lot of flexibility if we get hardware donated to us.