The disk system is the most important resource for a database. Since it is the only moving part in a computer, it is also the most prone to failure. Reliability aside, a disk is the slowest resource on a host-based system, and it is the point where all data resides.
There are three overall goals for a database administrator in terms of disk resources. They are:
Quantity — Having enough disk space to store what you need
Reliability — Having reliable disks so your data will remain available to users
Performance — Having the correct number and maximum speed for your disks to meet your throughput needs
These goals sound simple, but it is not always easy to plan for growth, or to know what hardware is both reliable and appropriate to meet your needs. With these goals in mind, this section examines the problems that might present roadblocks to fulfilling each of these goals.
Quantity — Having enough disk space to store what you need
