Some customers require that their application databases be available all the time. However, in these situations there is the concern that hardware or system failure could render the databases unavailable. To address this potential problem, SQL Server provides fallback support, which enables another computer that is running SQL Server to adopt the crucial databases and device files of a failed primary server. SQL Server's fallback functionality is based on underlying hardware or operating system support for transferring the control of the hard drive array from a primary server to a fallback server.