Microsoft® SQL Server 2012 Unleashed

Hardware Factors

You need to start by addressing your basic hardware issues for high availability and fault tolerance. This includes redundant power supplies, UPS systems, redundant network connections, and ECC memory (error correcting). Also available are “hot-swappable” components, such as disks, CPUs, and memory. In addition, most servers are now using multiple CPUs, fault-tolerant disk systems such as RAID, mirrored disks, storage area networks (SANs), Network Attached Storage (NAS), redundant fans, and so on.

Cost may drive the full extent of what you choose to build out. However, you should start with the following:

Redundant power supplies ...