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100% Uptime. Is It Really Possible? By Rollie Hawk< ONE OF THE TOUGHEST THINGS about consulting one’s clients is answering important questions. It’s not tough so much because the answers are hard to find—after all, we’re all experts in our professional fields—but rather because answers are complex. Most of us are constantly working to be forthright and honest in our answers while at the same time starting each and every one with that huge sellout of a qualifier, “well, it depends.” 34 Ping! Zine Magazine When it comes to hosting websites, data, or applications for clients, one of the toughest questions we face relates to what kind of uptime guarantees we can give. Obviously, fifty, seventy-five, and even ninety percent aren’t good enough for any clients, but how many nines can we realistically provide? Even more importantly, if we can—as so many hosts do—assert guarantees of 99%, 99.9%, and 99.99%, why not 100% uptime? So is 100% uptime really possible?
In the interest of being forthright and honest with you the reader, well, it indeed depends. THE REAL ANSWER Before going any further, let’s examine the real answer. At the risk of giving away the conclusion to our main question, if we know what our realistic goal can be, it’s easier to get there. The main thing that “depends” in this case comes down to a definition. When we say “100%” uptime, what do we really mean? That may sound like an absurd notion, as most people look at 100% as a specific concept with an exact value. But when arithmetical math gives way to statistics, numbers mean different things; and make no mistake about it, we’re dealing with statistics when it comes to any guarantee in the business world. In normal conversation, 100% means exactly, completely, totally, and entirely 100%. But in business, we’re looking at statistics. Unfortunately, when it comes to statistics there is no such thing as a guarantee. It follows that with the complex set of variables determining uptime, there is no such thing as a true 100%. Sorry, but that’s a fact. That said, the other side of the statistical coin is that guarantees (in the statistical sense) are not necessary. Rather, it’s a matter of making the calculations and adjustments required to get the probability of the desired result where we want it with as small a margin of error as possible. THE LIGHT-SPEED ANALOGY If you hate math and statistics, here’s another way of looking at this. If you are a fan of science fiction or ever thought about the possibility of mankind colonizing other solar systems, you eventually learned a disappointing reality: the universe comes with a built-in speed limit. Wormholes, warp drive, and string theory not withstanding, nothing in this universe can travel faster than the speed of light. Even worse, because of the effects of relativity, we can never reach that top speed in any vessel. We can, however, get as close to that speed as we want. Now as “out there” as that example may sound, it leads to an important analogy. Even though we can never literally achieve 100% uptime, we can get as close as we want. So if you need 99.9%, 99.99%, or even 99.9999% and on, it can theoretically be done. You can extend those nines as far as your infrastructure, budget, and other factors can possibly go. Eventually, the difference between your actual uptime and 100% gets so small that there is no real way to measure it effectively. ABOUT THOSE “NINES” Before considering any sort of uptime guarantee, it’s important to examine exactly what those percentages work out to in terms of actual minutes and seconds. There are a lot of hosts out there making promises that they haven’t really analyzed and a lot of hosting clients who have never considered how long that downtime can actually be, so let’s look at the actual amounts here. If we take our target uptime as a percent and subtract it from 100%, the result is the maximum downtime we are willing to accept in terms of percentages. For example, 99.9% uptime leaves 0.1% downtime. An average month is approximately 2.5 million seconds long. Once we have our maximum downtime percentage, we can multiply that by the number of seconds in a month to get our maximum downtime in seconds. For example, 0.1% of downtime multiplied by 2.5 million seconds works out to 2500 seconds or approximately 42 minutes. Table 1 – Conversions of “Nines” to Approximate Downtime “Nines” 1 2 3 4 5 6 Uptime % 90.0000% 99.0000% 99.9000% 99.9900% 99.9990% 99.9999% Downtime % Downtime (Sec) Approx. Downtime 10.0000% 1.0000% 0.1000% 0.0100% 0.0010% 0.0001% 250,000.0 25,000.0 2,500.0 250.0 25.0 In looking at what our uptimes work out to in terms of possible downtime (see Table 1), it comes clear that uptime percentage becomes much less arbitrary. In fact, if you look at the resulting downtimes, you’ll find that adding just one “nine” to your uptime guarantee results in magnitudes of difference in the practical measurement of downtime. WHAT CAN REASONABLY BE ACCOMPLISHED IN THAT TIME? Now that we know what we are looking at in terms of actual downtime, let’s perform a mental exercise. Considering the downtime we have available, let’s think about what can really be accomplished in those increasingly small windows of time. While nobody today would guarantee only 90% uptime, let’s start there. That works out to around three days of downtime. In three days, a web host could overnight ship a new server, install the operating system and software, configure everything, and restore from a tape. Though this is an extreme case, it gives one an idea of how much time can be saved just by having extra hardware around. Moving up to 99% uptime, we are giving ourselves around 7 hours. That’s reasonably enough time to replace a failing drive and restore from a backup tape. With 99.9% uptime, things start to get a lot tighter. Now that we are down to around 42 minutes, response time starts to play a big role. If you are a hosting company with a two- or three-person staff, you’d better be making sure someone is answering the phones and checking the email and support tickets at all times because in 42 minutes there’s no time for anyone to be away from the desk for lunch or a nap and still have time to get back and respond in the allotted time. Assuming you are on the ball, in 42 minutes you can reasonably troubleshoot a hardware issue and either replace a bad part or move a drive to another machine. You also may—and I say “may” very loosely—be able to make a change to DNS records and have the change propagated before too many people notice. Moving to 99.99% from 99.9% uptime is probably the most drastic jump in terms of how it affects a web host. In a timeframe of four minutes, there’s not much that can be done in terms of troubleshooting and repairs. At this point, any web host had better have some heavy-duty network management software in place that will page or e-mail techs as soon as there is a problem. About the most anyone can do in four minutes is reboot a server or router, and that’s assuming the problem is found in less than a minute or so. Once your guarantee moves above 99.99%, you are essentially moving from manned to primarily unmanned management of server and network issues. With only seconds to operate, management software could possibly edit a routing table or restart a single service on a server. This is where redundancy in terms of connections, load balancing, and clustering are absolutely [continued] www.pingzine.com 35 2.5 3 Days 7 Hours 42 Minutes 4 Minutes ½ Minute 2.5 Seconds
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