Server consolidation increases the effective utilization of server hardware by allowing one physical server to host multiple virtual machine (VM) instances. Most traditional non-virtualized servers are only utilized at 5% to 10% of their total computing capacity. By adding a virtualization platform to the server (such as Citrix XenServer, VMware vSphere or Hyper-V in Windows Server 2008 R2), the server can operate its original workload as a virtual machine, and host additional virtual workloads simultaneously -- often increasing the total utilization of the physical server from 50% to 80% of its total computing capacity.
But computing efficiency through consolidation is only one benefit of
Server consolidation with virtualization allows the flexibility to seamlessly migrate workloads between physical servers -- literally moving workloads at-will or as-needed. For example, a traditional server would have to be taken offline for maintenance or upgrades. With virtualization, all of the server's consolidated workloads can be migrated to a spare server or distributed amongst other servers, and then the original server can be shut down without any disruption to the workloads. Once the work is completed, the workloads can be migrated back to the original hardware. Workloads from a failing server can likewise be failed over or restarted on other servers, minimizing the effect of hardware problems.
Virtualization is also a boon to data protection, and workloads consolidated with virtualization can easily be copied with periodic point-in-time snapshots or replicated to off-site storage systems with little (if any) of the performance penalty experienced with traditional tape backup systems.
Even with a wealth of benefits, however, successful server consolidation requires a careful server consolidation strategy. First, consolidation should be approached in phases. Start by virtualizing and consolidating non-critical or low-priority workloads. Administrators can gain valuable experience with server consolidation tools. Then With more experience, you can then systematically virtualize and consolidate more important workloads until you tackle the most mission-critical applications.
The distribution of those virtualized workloads can make a tremendous difference in the success of your consolidation project. Since each workload can demand different computing resources, it's important to measure the needs of each workload and allocate workloads tso that the underlying host servers are not overloaded -- a process known as "workload balancing.". For example, it's often better to distribute CPU-intensive workloads on different servers rather than putting them on the same server. This prevents resource shortages that can cause workload performance or stability problems.
Stephen J. Bigelow is a senior technology writer in the DataCenter and Virtualization Group
This was first published in October 2009