Dec 22
Live Migration to Reduce Downtime
Eric Inch
I enjoy learning, using and helping others through technology. This is my second year with C/D/H after many years of consulting for numerous small and mid-sized companies. I enjoy challenging projects and continual improvement in all areas. Most recently, I have been working to help grow the virtualization practice at C/D/H and hopefully add that area to the already impressive expertise in infrastructure consulting at C/D/H.
When I’m not working, I enjoy spending time with my family. I have two little girls who keep me extremely busy but are always the highlight of my day.
For a more in-depth bio and a list of my areas of expertise, please visit http://www.cdh.com.
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Articles by Eric Inch
Virtualization can offer incredible advantages to your infrastructure. A server consolidation project can greatly increase the efficiency of your physical servers which routinely run between 3 and 10 percent utilization (what a waste!). It can also provide cost savings in reduced cooling and power requirements. Add in time savings for your IT department to provision new servers and the increased availability using High Availability (HA) capabilities and you are looking at a no-brainer.
One of the main benefits of the leading virtualization platforms is the ability to perform live migrations of running virtual machines. Live migration means you have the ability to take a virtual machine running on one host and move it to another host without downtime or disruption in service. This is usually done to perform maintenance on a physical server or to load balance virtual machines across a pool of hosts. Having the ability to migrate a VM while it is running significantly decreases the amount of downtime for your servers.
In the October C/D/H Technology Briefing titled “It’s a Virtual World We Live In”, I discussed the live migration capabilities of VMware ESX Server and Citrix XenServer. Both of these products are robust virtualization platforms and have a plethora of management capabilities. For live migration, Citrix has XenMotion and VMware has VMotion. Both solutions have similar requirements in that the hosts need similar and compatible processors, access to the same shared storage, and access to the same network.
The live migration process works by transferring the initial state of a virtual machine over to the destination. While this transition is taking place, all memory transactions are being recorded in a memory bitmap. After the initial state is completely copied to the target host, the source VM is suspended while the bitmap of changed memory is merged into the destination VM and brought online. The very last operation is a ping to the network to update the location of the VM’s MAC address. The final memory copy and ARP update happens in less than two seconds.
When determining the requirements for your virtualization project, I highly recommend you consider a solution that has the ability for live migration of virtual machines between hosts. This feature may increase the overall cost of the licensing for your virtual environment, but will most likely reap immediate benefits.