99.999% Uptime is difficult to achieve and may not be worth the cost.
From the table below, your website would be unreachable for only 5 minutes a year if you are to be called 5 nines or 99.999% available.
| Uptime (%) | Downtime |
|---|---|
| 90% | 876 hours (36.5 days) |
| 95% | 438 hours (18.25 days) |
| 99% | 87.6 hours (3.65 days) |
| 99.9% | 8.76 hours |
| 99.99% | 52.56 minutes |
| 99.999% | 5.256 minutes |
| 99.9999% | 31.536 seconds |
It’s very difficult to be 99.999% available.
If you have a hard disk error do you think you could fix it within 5 minutes each year ? probably not. You would need a second system that can step in at times of failure, this backup system would need to copy anything that could possibly fail.
You would also need to think about how quickly you can switch from your failed system to your backup.
It’s expensive and the money may be better spent elsewhere.
You can use a company or service to configure a high availability system that would meet the needs for 99.999% uptime. But, they are not cheap, high availability systems are complex and require expensive technical skills.
Some sites would benefit from expenditure in areas such as usability, performance and design first. Although if your site does go down, an error page that offers to inform the customer when the site is back up would be a nice addition to many sites.
Your customers may not mind lower downtime
Do your customers really need your service to be 99.999% available ?. For most sites I suspect the answer is no, especially when the costs of supplying such availability are taken into account.
Anonymous wrote,
True for non-mission-critical applications. However, there are many applications in the financial and other areas in which a lost transaction could mean millions of dollars of loss. Others, such as a patient monitoring system or a 911 system, could result in loss of life or property. These applications require extreme levels of availability - sometimes six nines or better. This level of availability can only be acheived with active/active systems.
Link | June 15th, 2006 at 8:14 am
Dan wrote,
Mission critical applications like the 911 system are run on multiple servers.
Should one the servers fail, the others share the load.
Link | October 6th, 2006 at 11:39 am
Jeff Rasmussen wrote,
Hospital systems have manual processes in place for monitoring patients.
Just recently, with the advent of Electronic Health records, hospitals do need high availability for the historical data to compare to the current data. The current data can and probably always will be available manually.
Most computer systems in hospitals are there for record keeping and are not as critical as one would think. Some areas, like Radiology, are changing that by collecting data electronically.
Link | October 13th, 2006 at 10:32 am
Blaxthos wrote,
Historically speaking, the concept of the five nines is traditionally applied to network availability. Ask any oldschool Bell employee — five nines was a gospel, and is very achievable.
Applying it to computer system uptime is a misappropriation of the term, and leads to misinformed essays discussing how “five nines is unachievable” appearing on blogs. Network downtime, especially realtime phone service and equipment, is measured in seconds (or in worst case, minutes) per year.
Link | January 29th, 2007 at 11:58 pm