A service level agreement is a contract in which the level of service to be provided is formally defined.May be specify performance,window of time,accuracy etc.A SLA is a legally binding document.
Threats to Data storage:Denial of Service
Denial of service is a cyber attack in which the perpetrator seeks to make a machine or network resource unavailable to it's intended users by temporarily or indefinitely disrupting services of a host connected to the internet.
+ Redundancy
+ Backups and Archives