SQL Server Recovery States

Question

When restoring a SQL Server Database, I notice that there are 3 different Recovery States to choose from:

• Restore with Recovery
• Restore with No Recovery
• Restore with Standby

I've always left it at it's default value, but what do they all mean?

(Preferably in layman's terms)

Answer 1

GateKiller,

In simple terms (and not a copy-paste out of the SQLBOL) so you can understand the concepts:

RESTORE WITH RECOVERY uses the backup media file (eg. fulldata.bak) to restore the database to back to the time that backup file was created. This is great if you want to go back in time to restore the database to an earlier state - like when developing a system.

If you want to restore the database TO THE VERY LATEST DATA, (i.e. like if your doing a system Disaster Recovery and you cannot lose any data) then you want to restore that backup AND THEN all the transaction logs created since that backup. This is when you use RESTORE NORECOVERY. It will allow you to restore the later transaction logs right up to the point of failure (as long as you have them).

RECOVERY WITH STANDBY is the ability to restore the database up to a parital date (like NORECOVERY above) but to allow the database still to be used READONLY. New transaction logs can still be applied to the database to keep it up to date (a standby server). Use this when it would take too long to restore a full database in order to Return To Operations the system. (ie. if you have a multi TB database that would take 16 hours to restore, but could receive transaction log updates every 15 minutes).

This is a bit like a mirror server - but without having "every single transaction" send to the backup server in real time.

Answer 2

You can set a Microsoft SQL Server database to be in NORECOVERY, RECOVERY or STANDBY mode.

RECOVERY is the normal and usual status of the database where users can connect and access the database (given that they have the proper permissions set up).

NORECOVERY allows the Database Administrator to restore additional backup files such as Differential or Transactional backups. While the database is in this state then users are not able to connect or access this database.

STANDBY is pretty much the same as NORECOVERY status however it allows users to connect or access database in a READONLY access. So the users are able to run only SELECT command against the database. This is used in Log Shipping quite often for reporting purposes. The only drawback is that while there are users in the database running queries SQL Server or a DBA is not able to restore additional backup files. Therefore if you have many users accessing the database all the time then the replication could fall behind.

Answer 3

From Books On line, i think it is pretty clear after you read it

NORECOVERY

Instructs the restore operation to not roll back any uncommitted transactions. Either the NORECOVERY or STANDBY option must be specified if another transaction log has to be applied. If neither NORECOVERY, RECOVERY, or STANDBY is specified, RECOVERY is the default.

SQL Server requires that the WITH NORECOVERY option be used on all but the final RESTORE statement when restoring a database backup and multiple transaction logs, or when multiple RESTORE statements are needed (for example, a full database backup followed by a differential database backup).

Note When specifying the NORECOVERY option, the database is not usable in this intermediate, nonrecovered state.

When used with a file or filegroup restore operation, NORECOVERY forces the database to remain in the restoring state after the restore operation. This is useful in either of these situations:

A restore script is being run and the log is always being applied.

A sequence of file restores is used and the database is not intended to be usable between two of the restore operations.

RECOVERY

Instructs the restore operation to roll back any uncommitted transactions. After the recovery process, the database is ready for use.

If subsequent RESTORE operations (RESTORE LOG, or RESTORE DATABASE from differential) are planned, NORECOVERY or STANDBY should be specified instead.

If neither NORECOVERY, RECOVERY, or STANDBY is specified, RECOVERY is the default. When restoring backup sets from an earlier version of SQL Server, a database upgrade may be required. This upgrade is performed automatically when WITH RECOVERY is specified. For more information, see Transaction Log Backups .

STANDBY = undo_file_name

Specifies the undo file name so the recovery effects can be undone. The size required for the undo file depends on the volume of undo actions resulting from uncommitted transactions. If neither NORECOVERY, RECOVERY, or STANDBY is specified, RECOVERY is the default.

STANDBY allows a database to be brought up for read-only access between transaction log restores and can be used with either warm standby server situations or special recovery situations in which it is useful to inspect the database between log restores.

If the specified undo file name does not exist, SQL Server creates it. If the file does exist, SQL Server overwrites it.

The same undo file can be used for consecutive restores of the same database. For more information, see Using Standby Servers.

Important If free disk space is exhausted on the drive containing the specified undo file name, the restore operation stops.

STANDBY is not allowed when a database upgrade is necessary.