A backup is a full or partial copy of the information in a database, held in a physically separate location. If the database becomes unavailable, you can restore it from the backup. You can use your backups to restore all committed changes to the database up to the time it became unavailable.
Backing up a running database provides a snapshot of the database where the data is in a consistent state, even though other users are modifying the database.
If the operating system or database server fails, or the database server does not shut down properly, then the database must be recovered. On database startup, the database server checks whether the database was shut down cleanly at the end of the previous session. If it was not, the database server runs an automatic recovery process to restore all changes up to the most recently committed transaction.
Backing up databases
Types of backup
Backup and recovery restrictions
Backup and recovery plan design
Backups for databases involved in synchronization and replication
The internal backup process
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