The pros and cons of using a virtualized machine
A virtualized machine can be a great help in maintaining a system, but the pros and cons of using one should always be taken into consideration.
A virtual machine is a computer that does not physically exist as a piece of hardware. The hardware that is seen by the operating system is emulated in an effort to separate the physical hardware from the operating system. This allows the virtual machine to be moved and hosted on any machine independent of hardware.
I'm often asked, "Why should I go virtual?" My first thought is why wouldn't you? I'll start out by listing the pros and cons of virtualization.
The pros of virtual machines
- Less physical hardware. In a typical distributed control system (DCS), you might have two Tag/OS servers, two batch servers, a historian or two, and an engineering station or two. Easily, you're looking at six servers that will need to be physically maintained. You'll find a time and overall cost savings on the replacement of hardware and maintenance.
- Central location to manage all assets. All of your virtual machines can be managed from one location.
- More eco-friendly. If you look at your current configuration, most of your machines are idling along. But, with them virtualized and running on a cluster, you maximize your machines' potential while saving money on energy costs.
- Disaster recovery is quick. Re-deploy virtual machines on your system (once you get the host machine back online) and you can have your system back up and running in no time.
- Expansion potentials. With the infrastructure in place, it's simply a matter of deploying a new machine and configuring. No need to go buy new servers (assuming you didn't cheap out and buy bottom-of-the-line servers).
- System upgrades. The time and heartache of making system images before applying a patch and having a system restore fail are all realities. With the virtual environment, if something goes wrong while applying a patch or update, you can simply roll back the virtual machine back where it was before you applied the patch using a snapshot.
- Software licensing. Many software packages (such as Rockwell products) tie a license key to a hard drive ID. In a virtual environment, the hard drive ID stays the same no matter which piece of hardware it is running on.
- Supports legacy operating systems. As hardware evolves and operating systems become obsolete, it's harder to find hardware and software that are compatible. Virtualizing these machines eliminates the operating system compatibility problems. This doesn't fix the problem of obsolete operating systems that are no longer supported-which is a security risk.
- Forward compatibility. As new hardware becomes available, your virtual machines can still run on this new hardware (as long as it is supported by the virtual host software).
- Use of thin clients. Using a thin client manager, replacement of a bad terminal is as easy as a few clicks and powering on the new unit. Conversely, with a physical machine you're stuck with re-imaging or building a replacement from scratch.
Many of the pros are related to the VMware ESXi/Sphere platform. The company has done a great job of packing high-availability features into its product:
- Monitors if a virtual machine has stopped running and restarts automatically (App High Availability).
- Can move a virtual machine running on one server to another without shutting down the guest virtual machine (VMotion).
- Can move a virtual machine running on one SAN to another without shutting down the guest machine (Storage VMotion).
- Automatically powers on a guest machine on boot of the server.
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