Twenty servers or four?
A company has 20 old servers. Each one uses power, takes space and needs cooling. Most of them are busy for only an hour a day.
The company moves them into virtual machines. A virtual machine is a computer made of software. Now four strong computers do the work of twenty. Is it always a good idea? No. In this lesson you look at the good points and the bad points.
Key words
| Word | What it means | Example |
|---|---|---|
| Virtual machine | A computer made of software. It runs inside a real computer. | A server in a file |
| Virtualisation | Making virtual versions of computers and their parts. | Four hosts, twenty servers |
| Disaster recovery | Getting the systems working again after a big failure, such as a fire. | Start the VMs at another site |
| Carbon footprint | The amount of carbon dioxide made by what we do. Less power means a smaller footprint. | Fewer machines, less power |
| Hypervisor | The software that makes and runs virtual machines. | The software that starts each guest |
| Snapshot | A saved copy of a virtual machine at one moment. You can go back to it. | Before a risky change |
| Overhead | Extra work that the computer does only to run the virtual layer. | CPU used by the hypervisor |
| Test environment | A safe copy of a system used to try changes before they go live. | A copy of the website |
| Container | A light, fast way to run one program in its own space. It shares the host's operating system. | A Docker container |
| Operating system | The main program that runs a computer. | Windows, Linux |
| Resilience | Being able to keep working, or recover fast, when something fails. | Move a VM to another host |
| CPU | The processor. It runs the instructions of a program. | The brain of a computer |
The cells students fill in are left blank in this preview.
Seven benefits
| Benefit | Why |
|---|---|
| Cost effective for large environments | Fewer machines to buy, house, power and cool |
| Easy to manage | One tool makes, copies, moves and removes many VMs |
| Resilience | A VM can move to another host if one host fails |
| Potentially lower carbon footprint | Fewer machines use less power. This depends on how well they are used. |
| Improved disaster recovery | A VM is a set of files, so it is easy to copy to another place and start again |
| Better testing environments | Make a copy, test, throw it away. Use snapshots to go back. |
| Education and training | Each learner has a safe machine of their own |
The cells students fill in are left blank in this preview.
Three drawbacks
| Drawback | Why |
|---|---|
| Extra hardware load | The hypervisor and each guest operating system use CPU, memory and storage. The host must be strong. |
| Slower execution | The program runs more slowly. There is an extra layer between the program and the hardware |
| A false picture of performance | A test in a VM may not match the real machine, because VMs share hardware and the layer adds delay |
The cells students fill in are left blank in this preview.
Quick check: good or bad?
Have a go
Quick check: good or bad?
4 questionsYour answers are marked here and are not kept. A college account keeps every student’s marks.
Worked example: is it cheaper?
Here are the numbers for the company in the hook. They are made up for this example.
Each old server costs 600 pounds a year to run: power, space and cooling. A strong host costs 1500 pounds a year to run. One host holds 5 virtual machines.
Worked example: the sums
| Step | Sum | Answer |
|---|---|---|
| Hosts needed for 20 servers | 20 divided by 5 (20 / 5) | 4 hosts |
| Cost of the old way | 20 times 600 (20 x 600) | 12000 pounds |
| Cost of the new way | 4 times 1500 (4 x 1500) | 6000 pounds |
| Saving each year | 12000 take away 6000 (12000 - 6000) | 6000 pounds |
The cells students fill in are left blank in this preview.