Maybe like me you are used to read architecture documents that state that an application should have high availability. It’s not uncommon to read that an application should have four-nine availability (99,99%). But what does it really mean ? In the JBoss in Action book there is a very clear explanation by giving the allowed downtime per year. Here is the table :
|
Uptime
|
Allowed downtime per year
|
| 99% | 87.6 hours |
| 99.9% | 8.8 hours |
| 99.99% | 53 minutes |
| 99.999% | 5.3 minutes |
| 99.9999% | 31 seconds |
| 99.99999% | 3.1 seconds |
3.1 seconds downtime per year, it’s really not a lot. So if you sign a contract with 99.99999% availability, make sure you have good lawers around you.
Filed under: Architecture
