Wastage of resources in Virtualization

Question

I am not sure if this is the write place to ask the question. However i hope it is.

When looking for a VPS earlier today, I was trying to understand how each container would work in the background. Keeping in mind the fact that the operating system uses most of the power and power on a system, wouldn't having multiple operating systems in the same machine mean more wastage of resources.

For instance if i was running centOS on a dedicated box and it was running lets say 20 background OS level processes. Then i go and install a virtualization platform and install 5 more centOS virtual machines in the same system which are exactly the same as the host operating system. Doesn't this mean duplication of those 20 processes 6 times? So internally the context switching is happening between 120 processes instead of 20?

Answer 1

Firstly your question seems to touch on two topics, full virtualization and paravirtualization. Most VPS are providing a paravirtualized environment which (to very broadly generalize) only virtualizes parts of the OS, it appears as a fully virtualized system to the user but in terms of processes, I/O, it can be very different depending on the OS and the way this has been implemented.

When dealing with full guest virtualization, the main reason and benefit of Virtualization is reclaiming underutilized resources. Making use of that idle capacity.

For example, 5 machines running at average resource utilization of 15% could be virtualized on a single server and use an average of 75% resources, still leaving 25% overhead to handle peak capacity.

If your processes can co-exist on the same system, all depend on the same libraries, configuration settings, etc. can be brought up/down and restarted without affecting each other - then you may "waste" resources virtualizing them.

However if you need to reboot/restart Server A without affecting Server B and they both have pretty low usage, or the two applications depend on different kernel versions for example - then that's a good candidate for virtualization.

When you move up to enterprise level virtualization and start thinking about computing costs in cents-per-hour and dollars-per-gigabyte then this "overhead" is nothing compared to the savings and other benefits. You don't have disks half empty, CPUs idling, wasted resources, competition for who gets to configure what. Virtual hosts can move between hosts depending on load, fault tolerance, high-availability, automated provisioning.