testing times

Some comments have wondered why it is that I should experience so much difficulty in my work with computers, even going so far as to suggest I move to a different type of job.

Well, you see, my job is to test computer systems, and so it is not surprising I find problems - because I go looking for them! I carry this attitude of "what happens if" to other activities outside of work. Instruction manuals and other documents get a critical eye from me, as do proposals by public figures.

Independent investigation of the truth is an important principle of the Baha'i Faith.

Never assume

I booked a trip to an indoor ski centre, for my first ever snowboarding lesson. Seeing that I am an absolute beginner, and the snow centre has a main slope and a smaller slope, I assumed our lesson would be on the smaller slope, or certainly at the lower part of the main slope. How wrong I was. The lesson was up towards the higher part of the main slope. And we started by learning to control ourselves using the toe edge of the board. That meant we were facing up the slope with our backs to the way we were travelling!

Working on a system the other week, I decided to use only one of the two application servers, since they were identical machines with the same software loaded, and I only needed one machine for the test. I checked the settings, the test script I had written, the processor load and the network connection, but all to no avail - the test always failed. Over a week later, I tried the other machine and the test took just 2 seconds to run correctly. The machines might have been identical, but one of them had a hardware failure!

And I tell my students always to list their assumptions, and always check that the assumptions are valid. Now I have slipped up twice within the same week. One of the principles of the Baha'i Faith is "Independent investigation of the truth".

Capacity planning

Two news items caught my attention this week. One of them was a report of a court case in America where, if I understood correctly, internet providers were being asked to keep a copy of every email and web page that passed through their systems. This put me to thinking about what that would mean in storage requirements. You see, testing a program does not just mean checking that the right text, icons and graphics are displayed, and clicking an icon performs the required action. Non-functional testing is looking at reliability, speed, and capacity.

So I started to think what is the storage requirement if an internet provider held a copy of all their traffic.

For one small provider with just two 64Mbit links, assuming that those links are mainly for business users (that is, traffic mostly between 8am and 6pm) with the links at just 75% of their capacity, then in one week the total traffic would be 64 * 0.75 * 3600 seconds in an hour * 10 hours * 5 days in Megabits. That comes to 8640000 Megabits (864 Gigabytes) per week. Of course, if the provider has a few hundred or thousand individual subscribers, each downloading emails, software and music files, and browsing the web looking for maps, video clips, reading and contributing to blogs, and so on every night then that figure could easily rise to double or triple that original estimate of 864Gb per week. Taken over the course of a year it approaches something of the order of 100 TerraBytes required for the storage.

If that is the figure for one small internet provider, just stop to think what the storage requirements will be for some of the larger providers who count their customers in the hundreds of thousands.

As you can see, bandwidth capacity and storage are important points to consider in planning any new service, or when upgrading an existing one.