These design features must preserve cached data if a system failure occurs. Caching controllers and disk subsystems can be safe for use by SQL Server. Most new purpose-built server platforms that incorporate these are safe. For performance reasons, SQL Server defers writes to the database via its own cache buffer system. They are not cached in the same manner as data writes.
Transactional integrity is one of the fundamental concepts of a relational database system.
Transactions are considered to be atomic units of work that are either totally applied or totally rolled back. The SQL Server write-ahead transaction log is a vital component in implementing transactional integrity. Any relational database system must also deal with a concept closely related to transactional integrity, which is recovery from unplanned system failure. On many database management systems, system failure may result in a lengthy human-directed manual recovery process. In contrast, the SQL Server recovery mechanism is completely automatic and operates without human intervention.