If you have looked at the websites of hosting providers on the web you can’t fail to have seen claims of 99.9%, 99.99% or even 99.999% uptime. The higher the number, the better the deal, right?
The answer is “not necessarily”
It all boils down to the SLA (Service Level Agreement). This is an agreement that the hosting business gives to its customer to keep their site online, or rather it is an agreement that the downtime will not exceed a certain threshold.
So what exactly is 99.9%, or 99.99%?
|Availability||Downtime per year||Downtime per month|
|99%||3.65 days||7.2 hours|
|99.9%||8.76 hours||43.8 mins|
|99.99%||55.5 mins||4.38 mins|
|99.999%||5.26 mins||25.9 seconds|
Looking at the above figures you can see how little time per month a site can be down in order not go over the SLA.
Ask yourself the question, when can they reboot a server, apply security patches etc? In Enterprise environments (Banks, Medical environments etc) there is a LOT of infrastructure in place, failover servers, mirrored storage, even backup data centres! In all but the most expensive hosting solutions you cannot expect this same level of SLA…. yet some places advertise it?
So… what’s the catch? Is it too good to be true?
In a word, yes. Most of these places cannot promise to have uptime to that level. Realistically most months they will probably manage it easily, but when something goes wrong (as it does for all companies, even Microsoft) then there will be downtime and it will be more than 4.38 mins a month!
So how can companies advertise an uptime level they cannot hit? Are they lying?
This is the clever (or sneaky?) part. An SLA is an “agreement”, not a promise. It means that if the agreed level is breached then the business will compensate the customer, be it in service credits or cash refund. The level of this is completely dependent on the business terms and conditions (or contract).
I have seen some hosting companies (no names) state “we will compensate downtime that is in excess of our SLA at our standard rate”. In this case it was a cloud provider that charged by the minute. In effect they were just saying that for every minute your server is offline you will be refunded a minute’s charge. So on that deal they may as well say they have a 100% uptime SLA, it makes no difference.
In Enterprise situations there are vast penalties for exceeding SLA’s, so a lot of thought and planning goes into meeting them, but in your general Internet hosting provider’s case they generally have small print to avoid high penalties, so they can get away will boasting about massive uptime SLA’s in order to bring in new business, without worrying about what happens if things go wrong.
So are we all doomed?
No, not at all. servers are generally quite reliable, and month on month most providers will hopefully give you 100% uptime. The way to judge a good hosting provider is not what uptime SLA they promise, but how they react when things go wrong. Do they react quickly, do they keep you informed, and do they solve the problem and explain why it happened if you ask?
A good web host is worth their weight in gold, just not for the simple reason of a 99.999% SLA.