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Backup & Recovery

In SQL Server, there are three types of backups:

  • Full Backup: Full backup means it will take the backup of the total .mdf file.

  • Differential Backup: Differential backup means it will take the backup of the extent's (8 pages= 1 extent) data which has been changed since last full backup. It is cumulative in nature and so is also called cumulative backup. cumulative means it will take backup from last full backup.

  • T-log Backup: T-log backup means it will backup the transaction log file. It is not cumulative in nature.
Now, there are three Recovery models in SQL server which are defined as:

  • Simple Recovery Model: In this recovery model, we can only have full backup and differential backup. If the data needs to be restored for the database having simple recovery model then last full backup will be restored first and after that the last differential backup. There will be no point in time recovery in this case.

  • Full Recovery Model: In this recovery model, we can have full backup, differential backup and T-log backup. If the data needs to be restored for the database having full recovery model then last full backup will be restored first then based on the requirement we can have differential or T-log restored. Point in time recovery is possible in this case. If we need circular property of the transaction log, we should take Tail log backup which also like T-log only. The only difference is that it will have the transactions upto the last time when database crashed.

  • Bulk Logged: When database is kept in bulk recovery model, it considers the data to be a single transaction. Modified extents will be there in log backup. Recovery for a point in time is possible in bulk logged if the transaction kept in bulk logged has already happened.
Note: You should always leave the database non operational while restore if you want to restore further differential or log backups. Otherwise, it will not allow you to do so.


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