Size Isn't Everything

November 13, 2008

A couple days ago, I took my daughter to her favorite store. We picked up a fair amount and on the way to the car she asked a simple question, or so I thought. “Why did they only fill these bags half way”. Confused I looked at the bags and realized she was holding a bag which had a large stuffed bear in it and was looking at a bag less than half full of canned food.

Being the person I am, rather than attempt to explain this to her I wanted to let her try and figure it out for herself so she would understand it better. When we got home, I filled the rest of the bag with cans and had her try and pick it up, as I expected the bag broke in her hands. I explained to her that the cans were much heavier then the bag. She still doesn’t quite understand the concept that the bag has 2 limits, size and weight but she is starting to understand this concept.

I thought about this story this morning when I started working on a project of determining how many containers a Virtuozzo server could handle based on its system requirements. Just like the bag, a Virtuozzo system has multiple limitations that need to be observed, the size of the containers as well as their “weight”. In this situation “weight” would be the drain on overall system resources. When attempting to determine how many containers a system can handle, you need to take into account not only how many will fit size wise, but also how much of the overall system resources each container will require.

It turns out this question is much easier to ask then to answer. You can take a small server such as a dual core with 4GB of RAM and put 20 or even 30 containers onto the server and have it run flawlessly when those containers are small and do not require much in the way of system recourses. At the same time however I can take a quad proc quad core with 64GB of RAM and grind it to a halt with 1 or 2 containers.

At the end of the day, I have found that you can make just about anything work, but before you attempt to determine what hardware you will need to run a Virtuozzo server, it’s a good idea to have an estimate of what you expect the containers to be doing. What could be worse than spending hours configuring a server and getting it online only to watch it grind to a halt because there are just too many containers completely saturating your system resources?