Use 99 times out of 100:

Keep systems and services 'available to users and processes' -- 99.9% of the time.

Availability is key for 'service-level agreements' (SLA) with a customer.
SLA is key to all entities that depend on systems being available "all the time."
Of key value are Internet services with an increased dependence on e-commerce.

If a server goes down then the down time cost can be high.

Every admin needs to maintain high availability of services at all times.

List all services and parts on an availability chart or a risk-assessment chart.

The following lists actions required to maintain high availability:
- Minimize the number of reboots of a server
- Clustering and server redundancy

Use redundant storage to avoid loss of data.

Recover from disasters by using remote and removable storage services to maintain reliable backups.

Plan to secure the system to avoid hackers, viruses, and other dangers.