The administrator is responsible for the integrity and availability of the data. This is a simple concept, but it is a huge responsibility. Some large corporations place a valuation on their data as high as $1 million per 100MB. The investment in dollars is not the only issue; many companies that lose mission-critical data simply never recover.
The actual job description for a system administrator varies widely. In small shops, the administrator might lay out the physical design, install SQL Server, implement the logical design, tune the installation, and then manage ongoing tasks such as backups. Larger sites might have tasks broken out into separate job functions. Managing users and backing up data are common examples of this. However, a lead administrator should still be in place to define policy and coordinate efforts. Whether performed by an individual or as a team, the core administration tasks are as follows:
Install and configure SQL Server
Plan and create databases
Manage data storage
Tune the database
Perform backup and recovery
Another task that is sometimes handled by administrators is that of managing stored procedures. As stored procedures for user applications often contain complex T-SQL code, they tend to fall into the realm of the application developer. However, because stored procedures are stored as objects in the database, they are also the responsibility of the administrator. If your application calls custom-stored procedures, you must be aware of this and coordinate with the application developers.
The system administration job can be stressful, frustrating, and demanding, but it is a highly rewarding, interesting, and respected position. You will be expected to know all, see all, and predict all, but you will be well compensated for your efforts.