Networking For Dummies
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The small amount of overhead imposed by virtualization is usually more than made up for by the simple fact that even the most heavily utilized servers spend most of their time twiddling their digital thumbs, waiting for something to do. In fact, many servers spend nearly all of their time doing nothing. As computers get faster and faster, they spend even more of their time with nothing to do.

Virtualization is a great way to put all of this unused processing power to good use.

Besides this basic efficiency benefit, there are several other compelling benefits to virtualization:

  • Hardware cost: You can typically save a lot of money by reducing hardware costs when you use virtualization. For example, suppose you replace ten servers that cost $4,000 each with one host server. Granted, you’ll probably spend more than $4,000 on that server, because it needs to be maxed out with memory, processor cores, network interfaces, and so on.

    So you’ll probably end up spending $15,000 or $20,000 for the host server. And you’ll end up spending something like $5,000 for the hypervisor software. But that’s still a lot less than the $40,000 you would have spent on ten separate computers at $4,000 each.

  • Energy costs: Many organizations have found that going virtual has reduced their overall electricity consumption for server computers by 80 percent. This savings is a direct result of using less computer hardware to do more work. For example, one host computer running ten virtual servers uses approximately one tenth of the energy used if each of the ten servers were run on separate hardware.

  • Recoverability: One of the biggest benefits of virtualization is not the cost savings, but the ability to quickly recover from hardware failures. For example, suppose your organization has ten servers each running on separate hardware. If any one of those servers goes down due to a hardware failure — say a bad motherboard — that server will remain down until you can fix the computer.

    On the other hand, if those ten servers are running as virtual machines on two different hosts and one of the hosts fails, the virtual machines that were running on the failed host can be brought up on the other host in a matter of minutes.

    Granted, the servers will run less efficiently on a single host than they would have on two hosts, but the point is that they’ll all be running after only a short downtime.

    In fact, with the most advanced hypervisors available, the transfer from a failing host to another host can be done automatically and instantaneously, so downtime is all but eliminated.

  • Disaster recovery: Besides the benefit of recoverability when hardware failures occur, an even bigger benefit of virtualization comes into play in a true disaster recovery situation.

    For example, suppose your organization’s sever infrastructure consists of 20 separate servers. In the case of a devastating disaster, such as a fire in the server room that destroys all hardware, how long will it take you to get all 20 of those servers back up and running on new hardware? Quite possibly the recovery time will be measured in weeks.

    In contrast, virtual machines are actually nothing more than files that can be backed up onto tape. As a result, in a disaster-recovery situation, all you have to do is rebuild a single host computer and reinstall the hypervisor software. Then you can restore the virtual machine backups from tape, restart the virtual machines, and be back up and running in a matter of days instead of weeks.

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