The HBA is the intelligent hardware residing on the host server which controls the transfer of data between the host and the target storage device.

A continuously available computer system is characterized as having essentially no downtime in any given year. A system with 99.999% availability experiences only about five minutes of downtime. In contrast, a high availability system is defined as having 99.9% uptime, which translates into a few hours of planned or unplanned downtime per year. 

Scaling by adding more machines to your pool of available resources.

A drive within a RAID setup which takes over automatically the functions and rebuilds the data if one of the hard drives within the RAID array fails. Once the failed hard drive is replaced it replicates the data back to this new drive and resumes its function as a spare.

This is a automatic management process, used in conjunction with a policy setup describing the importance of data within an organization. This process then moves older unused data onto a cheaper form of long term storage, e.g. accounts older than 5 years automatically moved from hard drive to tape.