Enterprise data protection and backup schemes range from the very simple to the very complex. In all but the simplest environments, you typically see a patchwork of software and hardware functionality layered together to prevent nearly any kind of data loss or corruption. Unfortunately, the technology deployed often defines the capabilities, rather than the business defining the capabilities that the technology must deliver. This is a dangerous trap to fall into -- both for you and for your organization.
Like an onion, a well-designed data protection scheme has many different layers, with functionality provided by different pieces of software and hardware. A wide range of technologies may come into play: SAN-to-SAN replication, SAN-provided storage snapshots, off-host backups, disk-to-disk backup, deduplication, virtual tape libraries, and server-based snapshots.
Some of this extra complexity is simply a result of the enterprise data explosion. As your pile of data grows, eventually you may reach a point where adding bigger and faster tape drives simply won't cut it. But the real driver for most backup complexity is a need to provide faster response to data loss and corruption events. Tape is great technology, and it won't disappear anytime soon, but it has comparatively poor recovery-point and recovery-time limitations that may make it ineffective as a sole solution.
So where do you start? Focus on your organization's needs first. The two biggest things to define before you buy are your RPO (recovery point objective) and RTO (recovery time objective).