VMware: Choosing Virtualization
Definitions
VMware VirtualCenter: software that manages a collection of physical VMware servers as one entity. VirtualCenter runs on a single server managing all the physical servers. The physical servers may be grouped into Virtual Datacenters.
Virtual Datacenter: a collection of physical servers managed by the VirtualCenter server. One VirtualCenter server may manage multiple Virtual Datacenters.
Virtual server (sometimes called a "virtual machine" or "VM"): a container in the VMware virtual center that emulates a physical server.
CIT has chosen VMware as the technology to provide virtual servers. Using VMware, a virtual server is created to meet a client's short or long-term server needs.
Installed applications and usage patterns determine if a particular server is a good candidate for virtualization.
- Ideal: Servers with occasional spikes of activity and long periods of inactivity.
- Acceptable: Web servers.
- Not acceptable: Computation and I/O intensive systems. Data warehouses that fully consume the server.
Virtual Servers are in a Shared Environment
Virtual servers use shared cycles and shared processors on a single machine. A virtual server contract for 2 processors guarantees 2 times as many cycles as a contract for 1 processor, but all of the cycles are shared. Depending on system usage, performance may vary.
Converting from a Physical Server to a Virtual Server
As CIT physical servers reach the end of their 4- or 5-year lifecycle, they should be evaluated as candidates for virtualization. If the decision is made to switch to a virtual server, migration is the same as migration to a new physical server. Automatic conversion tools, such as VMware Converter (formerly called P2V), are available, but will not be used because the transition from physical to virtual server is an ideal time to clean up a machine and be sure the new set up is well-designed.
Even though the server is virtual, migration to new supported operating systems is still required periodically as older operating systems are no longer supported. This is similar to the upgrade schedule on a physical server.
Maintenance Requirements
Maintenance of Virtual Servers
The operating system on the virtual server is maintained on the same schedule as that of physical servers. This usually requires scheduled down times to install patches. More information is available on the Windows Patch Management or the Unix Patch Management pages.
Maintenance of Underlying Virtual DataCenter
The high availability options outlined below allow virtual servers to be moved while the underlying physical server is upgraded and maintained. There should be no server interruption during maintenance and upgrades.
High Availability
The current VMware Virtual DataCenter has 3 physical servers that are each connected to the tier 1 and tier 2 networks for redundancy. Virtual servers can be transparently moved between these physical hosts so that the VMware physical servers and operating systems can be maintained and upgraded. For customers who request a high availability setup, if one of the physical VMware servers fails, the virtual servers are automatically moved to another physical VMware server.
Virtual servers can also move between buildings. Although the VMware physical servers are split between Rhodes and CCC, currently there is no data storage in CCC. If Rhodes is lost, the the VMware virtual center service will be unavailable. CIT plans to add data storage to CCC in 2009.
See the High Availability Options and Disaster Recovery page for more information about current options.
Costs
See the Supported Hardware page for information about costs.