Estimating the Availability of Simple Systems

As system managers, we are tasked with building and maintaining systems that are expected to be ‘always on’. Our objective of course, is to bridge the gap between our users definition of ‘always on’ and our accountants definition of ‘under budget’. In my experience, the gap tends to be large.

With that goal in mind, I’ve outlined a method for quickly estimating expected availability for simple systems, or ‘application stacks’. For purposes of these posts, a system includes power, cooling, WAN, network, servers and storage.

The introductory post outlines the basics for estimating the availability of simple systems, the assumptions used when estimating availability, and the basics of serial, parallel and coupled dependencies.

Part one covers estimating the availability of simple non-redundant systems.

Part two covers estimating the availability of systems with simple active/passive redundancy.

My hope is that there prove useful as rules of thumb for bridging the gap between user expectations and the realities of the systems on which they depend.

The Pew Broadband Report and the Digital Divide

The digital divide appears to be more complicated than we thought. From the 2008 Pew Home Broadband Report it looks like only a fraction of non-Internet users are actually held back by the availability of broadband. A whole bunch of non-users are simply not interested, and another large group  doesn't have the money.  The plethora of task forces that meet to talk endlessly about the digital divide need to think about cost and interest, not just availability.

Among people who do not use the Internet (27% of adult Americans)

• 43% of non-internet users are over the age of 65 or, put differently, 65% of senior citizens do not use the internet.
• 43% of non-internet users have household incomes under $30,000 per year.

When asked why they don’t use the internet:

• 33% of non-users say they are not interested.
• 12% say they don’t have access.
• 9% say it is too difficult or frustrating.
• 7% say it is too expensive.
• 7% say it is a waste of time.

So we have an age problem, which will eventually will resolve itself (Old people tend to go away eventually),  an income problem, and a simple lack of interest.  A large number of people, 33% + 7% of those who are not connected simply don't want to be connected. Apparently we have not created a compelling reason to convince the un-interested people that the Internet has value. A small number of Internet users are still using dial up. And among dial-up users:

Among the 10% of Americans (or 15% of home internet users) with dial-up at home:

• 35% of dial-up users say that the price of broadband service would have to fall.
• 19% of dial-up users said nothing would convince them to get broadband.
• 10% of dial-up users – and 15% of dial-up users in rural America – say that broadband service would have to become available where they.

So the issue of converting dial up users to broadband is not simply that broadband isn't available (10%). The largest segment of the dial up population is waiting for the price to drop. The second largest segment isn't going to get broadband no matter what. This is not an availability issue, it is a cost issue and an I don't care issue.

In any case, a number of potential Internet users are still using dial-up, not broadband. If you take dial up users and lump them in with mobile and PDA users, you have a class of people that have Internet access, but the access is restricted in some way, either by bandwidth or device capability. Call them 'low capability users'. Low bandwidth dial up users are shrinking, but low capability device users are growing (mobile phone, PDA, and iPhone users). If you develop applications, you need to keep the low capability users on the radar. They are not going to go away.

The BBC figured this out. I can access the majority of their content with low bandwidth, low capability GPRS or EDGE devices, with high bandwidth devices, and with everything in between. They get it.

The bottom line is that a segment of your users are, and for the foreseeable future will be using low capability devices, either dial-up, mobile, PDA or iPhones. If those users are not able to use an application, they are excluded not by the device or Internet access technology that they choose to use, but rather by the application or site design that excludes those users.

Accident

 

It's the end of a long day, I'm a thousand miles from home, on a rural Montana road driving not too far over the speed limit. There is nothing around - except - what's that?

The neural net kicks in. Somewhere in the vast emptiness between my ears, the pattern matching algorithm registers a hit, the bell dings, the right leg stomps the middle pedal, the left leg stomps the left pedal, the ABS brakes kick in, the flashers go on and the Subaru stops. In the ditch is a person kneeling, a lump of something potentially sentient, and a badly bent motorcycle, wheels up.

Yep - I'm first on the scene of a motorcycle accident. They aren't hard to recognize, especially if you've seen a whole bunch of them during your motorcycle road racing phase.

Now what the heck do I do? I'm not trained in anything like first aid. The only rule I could remember from high school first aid is 'Remain Calm'. Ok - I'm calm, now what? What's rule number two?  Damn - can't remember.

A quick survey - the victim is breathing, conscious, alert, but with various limbs pointing in non-standard directions. There are no fluid leaks. Presumably she is going to be OK, but she certainly isn't going to move until someone with proper equipment gets on the scene. The victims husband is already calling 911, so that is covered. Just about the time that I'm figuring I'm going to have to actually do something, help arrives. Not the official help from 911, but rather a Pennsylvania tourist-lady, who just happens to be an EMT, a paramedic, an emergency room nurse. Whew.......

The paramedic/tourist (name forgotten) took charge, did basic  analysis, and gave me something useful to do (keep the victim from hurting herself any worse, hold her head and keep her from moving....). The first pass at a diagnosis - one busted arm, one dislocated hip, and no other serious injuries.

Now the motorcycle road racing experience gets relevant. I remember that post-crash, one doesn't feel pain. They tell me that adrenalin from the crash masks the pain - for a while. (In one of my own crashes, I remember arguing with the paramedic about the extent of my injury. He insisted my shoulder was dislocated, I insisted it wasn't. He was right. I couldn't feel it - the adrenalin numbed me.)

Unfortunately for the crash victim, the adrenalin pain mask didn't last long enough. A few minutes later, the pain kicked in. And the victim, in obvious severe pain, did what bikers do - she gritted her teeth and took the pain as it came. She's tough, real tough.

I'm pretty sure that in rural Montana, most or all of the emergency workers are volunteers. The volunteers arrived, some directly from home in their personal vehicles, others with the official ambulance. The first thing they did was a neck brace. Preventing neck/back damage seems to be priority - at least it is if the person is breathing, beating and not leaking too badly. I got the privilege of assisting on the neck brace. Then - with the ditch full of people who know what to do, and the road full of shiny, expensive vehicles with flashing lights, I bailed.

The Pennsylvania tourist-lady? She was cool - on the way back to the cars, she admitted that she did emergency work for the thrill. She lived to help people, and to get a rush doing it.

I wonder if the victim had insurance?