Uptime

Uptime is the percentage of time that a system is available and usable. An uptime of 99.9 per cent sounds almost perfect, but it still means nearly nine hours of downtime a year. So the figures after the decimal point matter.

For the systems your business runs on, availability is not a detail. If your ordering system or your till goes down, work stops and you immediately lose money and trust. The more critical a system, the higher the uptime you can expect.

High availability comes at a price. Every step closer to a hundred per cent calls for extra investment in backupA spare copy so your data doesn't get lost. systems and maintenance. The art is to decide for each system how much availability you really need, and not to aim blindly above that.