BACKUP (Transact-SQL)

Backs up a SQL database.

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SQL Server

Backs up a complete SQL Server database to create a database backup, or one or more files or filegroups of the database to create a file backup (BACKUP DATABASE). Also, under the full recovery model or bulk-logged recovery model, backs up the transaction log of the database to create a log backup (BACKUP LOG).

Syntax

--Back up a whole database
BACKUP DATABASE { database_name | @database_name_var }
  TO <backup_device> [ ,...n ]
  [ <MIRROR TO clause> ] [ next-mirror-to ]
  [ WITH { DIFFERENTIAL
           | <general_WITH_options> [ ,...n ] } ]
[;]

--Back up specific files or filegroups
BACKUP DATABASE { database_name | @database_name_var }
 <file_or_filegroup> [ ,...n ]
  TO <backup_device> [ ,...n ]
  [ <MIRROR TO clause> ] [ next-mirror-to ]
  [ WITH { DIFFERENTIAL | <general_WITH_options> [ ,...n ] } ]
[;]

--Create a partial backup
BACKUP DATABASE { database_name | @database_name_var }
 READ_WRITE_FILEGROUPS [ , <read_only_filegroup> [ ,...n ] ]
  TO <backup_device> [ ,...n ]
  [ <MIRROR TO clause> ] [ next-mirror-to ]
  [ WITH { DIFFERENTIAL | <general_WITH_options> [ ,...n ] } ]
[;]

--Back up the transaction log (full and bulk-logged recovery models)
BACKUP LOG
  { database_name | @database_name_var }
  TO <backup_device> [ ,...n ]
  [ <MIRROR TO clause> ] [ next-mirror-to ]
  [ WITH { <general_WITH_options> | <log_specific_options> } [ ,...n ] ]
[;]

--Back up all the databases on an instance of SQL Server (a server)

ALTER SERVER CONFIGURATION
SET SUSPEND_FOR_SNAPSHOT_BACKUP ON
[;]

BACKUP SERVER
  TO <backup_device> [ ,...n ]
  [ <MIRROR TO clause> ] [ next-mirror-to ]
  [ WITH { METADATA_ONLY
           | <general_WITH_options> [ ,...n ] } ]
[;]

--Back up a group of databases
ALTER DATABASE <database>
SET SUSPEND_FOR_SNAPSHOT_BACKUP ON

ALTER DATABASE <...>
SET SUSPEND_FOR_SNAPSHOT_BACKUP ON
...

BACKUP GROUP {<database> [,... ]}
  TO <backup_device> [ ,...n ]
  [ <MIRROR TO clause> ] [ next-mirror-to ]
  [ WITH { METADATA_ONLY
           | <general_WITH_options> [ ,...n ] } ]
[;]

<backup_device>::=
 {
  { logical_device_name | @logical_device_name_var }
 | {   DISK
     | TAPE
     | URL } =
     { 'physical_device_name' | @physical_device_name_var | 'NUL' }
 }

<MIRROR TO clause>::=
 MIRROR TO <backup_device> [ ,...n ]

<file_or_filegroup>::=
 {
   FILE = { logical_file_name | @logical_file_name_var }
 | FILEGROUP = { logical_filegroup_name | @logical_filegroup_name_var }
 }

<read_only_filegroup>::=
FILEGROUP = { logical_filegroup_name | @logical_filegroup_name_var }

<general_WITH_options> [ ,...n ]::=
--Backup Set Options
   COPY_ONLY
 | [ COMPRESSION [ ALGORITHM = { MS_XPRESS | accelerator_algorithm } ] | NO_COMPRESSION ]
 | DESCRIPTION = { 'text' | @text_variable }
 | NAME = { backup_set_name | @backup_set_name_var }
 | CREDENTIAL
 | ENCRYPTION
 | FILE_SNAPSHOT
 | { EXPIREDATE = { 'date' | @date_var }
        | RETAINDAYS = { days | @days_var } }
 | { METADATA_ONLY | SNAPSHOT }

--Media Set Options
   { NOINIT | INIT }
 | { NOSKIP | SKIP }
 | { NOFORMAT | FORMAT }
 | MEDIADESCRIPTION = { 'text' | @text_variable }
 | MEDIANAME = { media_name | @media_name_variable }
 | BLOCKSIZE = { blocksize | @blocksize_variable }

--Data Transfer Options
   BUFFERCOUNT = { buffercount | @buffercount_variable }
 | MAXTRANSFERSIZE = { maxtransfersize | @maxtransfersize_variable }

--Error Management Options
   { NO_CHECKSUM | CHECKSUM }
 | { STOP_ON_ERROR | CONTINUE_AFTER_ERROR }

--Compatibility Options
   RESTART

--Monitoring Options
   STATS [ = percentage ]

--Tape Options
   { REWIND | NOREWIND }
 | { UNLOAD | NOUNLOAD }

--Encryption Options
 ENCRYPTION (ALGORITHM = { AES_128 | AES_192 | AES_256 | TRIPLE_DES_3KEY } , encryptor_options ) <encryptor_options> ::=
   SERVER CERTIFICATE = Encryptor_Name | SERVER ASYMMETRIC KEY = Encryptor_Name

<log_specific_options> [ ,...n ]::=
--Log-specific Options
   { NORECOVERY | STANDBY = undo_file_name }
 | NO_TRUNCATE

Arguments

DATABASE

Specifies a complete database backup. If a list of files and filegroups is specified, only those files and filegroups are backed up. During a full or differential database backup, SQL Server backs up enough of the transaction log to produce a consistent database when the backup is restored.

When you restore a backup created by BACKUP DATABASE (a data backup), the entire backup is restored. Only a log backup can be restored to a specific time or transaction within the backup.

Note

Only a full database backup can be performed on the master database.

LOG

Specifies a backup of the transaction log only. The log is backed up from the last successfully executed log backup to the current end of the log. Before you can create the first log backup, you must create a full backup.

You can restore a log backup to a specific time or transaction within the backup by specifying WITH STOPAT, STOPATMARK, or STOPBEFOREMARK in your RESTORE LOG statement.

Note

After a typical log backup, some transaction log records become inactive, unless you specify WITH NO_TRUNCATE or COPY_ONLY. The log is truncated after all the records within one or more virtual log files become inactive. If the log is not being truncated after routine log backups, something might be delaying log truncation. For more information, see Factors that can delay log truncation.

GROUP (<database>,...n)

Introduced in SQL Server 2022 (16.x).

Back up a group of databases. Uses snapshot backup. Requires WITH METADATA_ONLY. See Create a Transact-SQL snapshot backup.

SERVER

Introduced in SQL Server 2022 (16.x).

Back up all databases on an instance of SQL Server. Uses snapshot backup. Requires WITH METADATA_ONLY. See Create a Transact-SQL snapshot backup.

METADATA_ONLY

Introduced in SQL Server 2022 (16.x).

Required for snapshot backup. BACKUP SERVER, or BACKUP GROUP... See Create a Transact-SQL snapshot backup.

METADATA_ONLY is synonymous with SNAPSHOT. Virtual device interface (VDI) uses SNAPSHOT. For information about VDI, see Virtual device interface (VDI) reference.

{ database_name | @database_name_var }

Is the database from which the transaction log, partial database, or complete database is backed up. If supplied as a variable (@database_name_var), this name can be specified either as a string constant (@database_name_var=database name) or as a variable of character string data type, except for the ntext or text data types.

Note

The mirror database in a database mirroring partnership cannot be backed up.

<file_or_filegroup> [ ,...n ]

Used only with BACKUP DATABASE, specifies a database file or filegroup to include in a file backup, or specifies a read-only file or filegroup to include in a partial backup.

FILE = { logical_file_name | @logical_file_name_var }

Is the logical name of a file or a variable whose value equates to the logical name of a file that is to be included in the backup.

FILEGROUP = { logical_filegroup_name | @logical_filegroup_name_var }

Is the logical name of a filegroup or a variable whose value equates to the logical name of a filegroup that is to be included in the backup. Under the simple recovery model, a filegroup backup is allowed only for a read-only filegroup.

Note

Consider using file backups when the database size and performance requirements make a database backup impractical. The NUL device can be used to test the performance of backups, but should not be used in production environments.

n
Is a placeholder that indicates that multiple files and filegroups can be specified in a comma-separated list. The number is unlimited.

For more information, see Full File Backups and Back Up Files and Filegroups.

READ_WRITE_FILEGROUPS [ , FILEGROUP = { logical_filegroup_name | @logical_filegroup_name_var } [ ,...n ] ]

Specifies a partial backup. A partial backup includes all the read/write files in a database: the primary filegroup and any read/write secondary filegroups, and also any specified read-only files or filegroups.

READ_WRITE_FILEGROUPS

Specifies that all read/write filegroups be backed up in the partial backup. If the database is read-only, READ_WRITE_FILEGROUPS includes only the primary filegroup.

Important

Explicitly listing the read/write filegroups by using FILEGROUP instead of READ_WRITE_FILEGROUPS creates a file backup.

FILEGROUP = { logical_filegroup_name | @logical_filegroup_name_var }

Is the logical name of a read-only filegroup or a variable whose value equates to the logical name of a read-only filegroup that is to be included in the partial backup. For more information, see "<file_or_filegroup>," earlier in this article.

n
Is a placeholder that indicates that multiple read-only filegroups can be specified in a comma-separated list.

For more information about partial backups, see Partial Backups.

TO <backup_device> [ ,...n ]

Indicates that the accompanying set of backup devices is either an unmirrored media set or the first of the mirrors within a mirrored media set (for which one or more MIRROR TO clauses are declared).

<backup_device>
Specifies a logical or physical backup device to use for the backup operation.

{ logical_device_name | @logical_device_name_var }

Applies to: SQL Server
Is the logical name of the backup device to which the database is backed up. The logical name must follow the rules for identifiers. If supplied as a variable (@logical_device_name_var), the backup device name can be specified either as a string constant (@logical_device_name_var= logical backup device name) or as a variable of any character string data type except for the ntext or text data types.

{ DISK | TAPE | URL} = { 'physical_device_name' | @physical_device_name_var | 'NUL' }

Applies to: SQL Server (URL starting with SQL Server 2012 (11.x) SP1 CU2)

Specifies a disk file or tape device, or a URL.

The URL format is used for creating backups to Microsoft Azure Blob Storage or S3-compatible object storage. For more information and examples, see:

• SQL Server Backup and Restore with Microsoft Azure Blob Storage. For a tutorial, see Tutorial: SQL Server Backup and Restore to Microsoft Azure Blob Storage.
• Backup and restore to S3-compatible storage was introduced in SQL Server 2022 (16.x), see SQL Server backup and restore with S3-compatible object storage. Also review the option for SQL Server backup to URL for S3-compatible object storage.

Note

The NUL disk device will discard all information sent to it and should only be used for testing. This is not for production use.

Important

Starting with SQL Server 2012 (11.x) SP1 CU2 through SQL Server 2014 (12.x), you can only backup to a single device when backing up to URL for Azure Blob Storage. In order to backup to multiple devices when backing up to URL, you must use SQL Server 2016 (13.x) and later and you must use Shared Access Signature (SAS) tokens. For examples creating a Shared Access Signature, see SQL Server Backup to URL and Simplifying creation of SQL Credentials with Shared Access Signature (SAS) tokens on Azure Storage with Powershell.

A disk device does not have to exist before it is specified in a BACKUP statement. If the physical device exists and the INIT option is not specified in the BACKUP statement, the backup is appended to the device.

Note

The NUL device will discard all input sent to this file, however the backup will still mark all pages as backed up.

For more information, see Backup Devices.

Note

The TAPE option will be removed in a future version of SQL Server. Avoid using this feature in new development work, and plan to modify applications that currently use this feature.

n
Is a placeholder that indicates that up to 64 backup devices might be specified in a comma-separated list.

MIRROR TO <backup_device> [ ,...n ]

Specifies a set of up to three secondary backup devices, each of which mirrors the backups devices specified in the TO clause. The MIRROR TO clause must specify the same type and number of the backup devices as the TO clause. The maximum number of MIRROR TO clauses is three.

This option is available only in the Enterprise edition of SQL Server.

Note

For MIRROR TO = DISK, BACKUP automatically determines the appropriate block size for disk devices based on the sector size of the disk. If the MIRROR TO disk is formatted with a different sector size than the disk specified as the primary backup device, the backup command will fail. In order to mirror backups to devices that have different sector sizes, the BLOCKSIZE parameter must be specified, and should be set to the highest sector size among all the target devices. For more information about block size, see "BLOCKSIZE" later in this topic.

<backup_device>
See "<backup_device>," earlier in this section.

n
Is a placeholder that indicates that up to 64 backup devices might be specified in a comma-separated list. The number of devices in the MIRROR TO clause must equal the number of devices in the TO clause.

For more information, see "Media Families in Mirrored Media Sets" in the Remarks section, later in this article.

[ next-mirror-to ]
Is a placeholder that indicates that a single BACKUP statement can contain up to three MIRROR TO clauses, in addition to the single TO clause.

WITH Options

Specifies options to be used with a backup operation.

CREDENTIAL

Applies to: SQL Server (starting withSQL Server 2012 (11.x) SP1 CU2).

Used only when creating a backup to Azure Blob Storage.

FILE_SNAPSHOT

Applies to: SQL Server (starting with SQL Server 2016 (13.x)).

Used to create an Azure snapshot of the database files when all of the SQL Server database files are stored using the Azure Blob Storage. For more information, see SQL Server Data Files in Microsoft Azure. SQL Server Snapshot Backup takes Azure snapshots of the database files (data and log files) at a consistent state. A consistent set of Azure snapshots make up a backup and are recorded in the backup file. The only difference between BACKUP DATABASE TO URL WITH FILE_SNAPSHOT and BACKUP LOG TO URL WITH FILE_SNAPSHOT is that the latter also truncates the transaction log while the former does not. With SQL Server Snapshot Backup, after the initial full backup that is required by SQL Server to establish the backup chain, only a single transaction log backup is required to restore a database to the point in time of the transaction log backup. Furthermore, only two transaction log backups are required to restore a database to a point in time between the time of the two transaction log backups.

DIFFERENTIAL

Used only with BACKUP DATABASE, specifies that the database or file backup should consist only of the portions of the database or file changed since the last full backup. A differential backup usually takes up less space than a full backup. Use this option so that all individual log backups performed since the last full backup do not have to be applied.

Note

By default, BACKUP DATABASE creates a full backup.

For more information, see Differential Backups.

ENCRYPTION

Used to specify encryption for a backup. You can specify an encryption algorithm to encrypt the backup with or specify NO_ENCRYPTION to not have the backup encrypted. Encryption is recommended practice to help secure backup files. The list of algorithms you can specify are:

• AES_128
• AES_192
• AES_256
• TRIPLE_DES_3KEY
• NO_ENCRYPTION

If you choose to encrypt, you will also have to specify the encryptor using the encryptor options:

• SERVER CERTIFICATE = Encryptor_Name
• SERVER ASYMMETRIC KEY = Encryptor_Name

The SERVER CERTIFICATE and SERVER ASYMMETRIC KEY are a certificate and an asymmetric key created in master database. For more information, see CREATE CERTIFICATE and CREATE ASYMMETRIC KEY respectively.

Warning

When encryption is used in conjunction with the FILE_SNAPSHOT argument, the metadata file itself is encrypted using the specified encryption algorithm and the system verifies that Transparent Data Encryption (TDE) was completed for the database. No additional encryption happens for the data itself. The backup fails if the database was not encrypted or if the encryption was not completed before the backup statement was issued.

Backup Set Options

These options operate on the backup set that is created by this backup operation.

Note

To specify a backup set for a restore operation, use the FILE = <backup_set_file_number> option. For more information about how to specify a backup set, see "Specifying a Backup Set" in RESTORE Arguments.

COPY_ONLY

Specifies that the backup is a copy-only backup, which does not affect the normal sequence of backups. A copy-only backup is created independently of your regularly scheduled, conventional backups. A copy-only backup does not affect your overall backup and restore procedures for the database.

Copy-only backups should be used in situations in which a backup is taken for a special purpose, such as backing up the log before an online file restore. Typically, a copy-only log backup is used once and then deleted.

• When used with BACKUP DATABASE, the COPY_ONLY option creates a full backup that cannot serve as a differential base. The differential bitmap is not updated, and differential backups behave as if the copy-only backup does not exist. Subsequent differential backups use the most recent conventional full backup as their base.

  Important

  If DIFFERENTIAL and COPY_ONLY are used together, COPY_ONLY is ignored, and a differential backup is created.

• When used with BACKUP LOG, the COPY_ONLY option creates a copy-only log backup, which does not truncate the transaction log. The copy-only log backup has no effect on the log chain, and other log backups behave as if the copy-only backup does not exist.

For more information, see Copy-Only Backups.

[ COMPRESSION [ ALGORITHM = ( { MS_XPRESS | accelerator_algorithm } ) ] | NO_COMPRESSION ]

Specifies whether backup compression is performed on this backup, overriding the server-level default.

At installation, the default behavior is no backup compression. But this default can be changed by setting the backup compression default server configuration option. For information about viewing the current value of this option, see View or Change Server Properties.

For information about using backup compression with Transparent Data Encryption (TDE) enabled databases, see the Remarks section.

COMPRESSION
Explicitly enables backup compression.

NO_COMPRESSION
Explicitly disables backup compression.

SQL Server 2022 (16.x) introduces ALGORITHM, which identifies a compression algorithm for the operation. The default is MS_XPRESS. If you have configured Integrated acceleration and offloading, you can use an accelerator provided by the solution. For example, if you have configured Intel® QuickAssist Technology (QAT) for SQL Server, the following example completes the backup with the accelerator solution, with QATzip library using QZ_DEFLATE with the compression level 1.

BACKUP DATABASE <database_name> TO DISK WITH COMPRESSION (ALGORITHM = QAT_DEFLATE) 

DESCRIPTION = { 'text' | @text_variable }

Specifies the free-form text describing the backup set. The string can have a maximum of 255 characters.

NAME = { backup_set_name | @backup_set_var }

Specifies the name of the backup set. Names can have a maximum of 128 characters. If NAME is not specified, it is blank.

{ EXPIREDATE ='date' | RETAINDAYS = days }

Specifies when the backup set for this backup can be overwritten. If these options are both used, RETAINDAYS takes precedence over EXPIREDATE.

If neither option is specified, the expiration date is determined by the media retention configuration setting. For more information, see Server Configuration Options.

Important

These options only prevent SQL Server from overwriting a file. Tapes can be erased using other methods, and disk files can be deleted through the operating system. For more information about expiration verification, see SKIP and FORMAT in this topic.

EXPIREDATE = { 'date' | @date_var }
Specifies when the backup set expires and can be overwritten. If supplied as a variable (@date_var), this date must follow the configured system datetime format and be specified as one of the following:

• A string constant (@date_var = date)
• A variable of character string data type (except for the ntext or text data types)
• A smalldatetime
• A datetime variable

For example:

• 'Dec 31, 2020 11:59 PM'
• '1/1/2021'

For information about how to specify datetime values, see Date and Time Types.

Note

To ignore the expiration date, use the SKIP option.

RETAINDAYS = { days | @days_var }
Specifies the number of days that must elapse before this backup media set can be overwritten. If supplied as a variable (@days_var), it must be specified as an integer.

{ METADATA_ONLY | SNAPSHOT }

Applies to: SQL Server 2022 (16.x)

METADATA_ONLY and SNAPSHOT are synonyms.

Media Set Options

These options operate on the media set as a whole.

{ NOINIT | INIT }

Controls whether the backup operation appends to or overwrites the existing backup sets on the backup media. The default is to append to the most recent backup set on the media (NOINIT).

Note

For information about the interactions between { NOINIT | INIT } and { NOSKIP | SKIP }, see Remarks later in this topic.

NOINIT
Indicates that the backup set is appended to the specified media set, preserving existing backup sets. If a media password is defined for the media set, the password must be supplied. NOINIT is the default.

For more information, see Media Sets, Media Families, and Backup Sets.

INIT
Specifies that all backup sets should be overwritten, but preserves the media header. If INIT is specified, any existing backup set on that device is overwritten, if conditions permit. By default, BACKUP checks for the following conditions and does not overwrite the backup media if either condition exists:

• Any backup set has not yet expired. For more information, see the EXPIREDATE and RETAINDAYS options.
• The backup set name given in the BACKUP statement, if provided, does not match the name on the backup media. For more information, see the NAME option, earlier in this section.

To override these checks, use the SKIP option.

For more information, see Media Sets, Media Families, and Backup Sets.

{ NOSKIP | SKIP }

Controls whether a backup operation checks the expiration date and time of the backup sets on the media before overwriting them.

Note

For information about the interactions between { NOINIT | INIT } and { NOSKIP | SKIP }, see "Remarks," later in this topic.

NOSKIP
Instructs the BACKUP statement to check the expiration date of all backup sets on the media before allowing them to be overwritten. This is the default behavior.

SKIP
Disables the checking of backup set expiration and name that is usually performed by the BACKUP statement to prevent overwrites of backup sets. For information about the interactions between { INIT | NOINIT } and { NOSKIP | SKIP }, see "Remarks," later in this article. To view the expiration dates of backup sets, query the expiration_date column of the backupset history table.

{ NOFORMAT | FORMAT }

Specifies whether the media header should be written on the volumes used for this backup operation, overwriting any existing media header and backup sets.

NOFORMAT
Specifies that the backup operation preserves the existing media header and backup sets on the media volumes used for this backup operation. This is the default behavior.

FORMAT
Specifies that a new media set be created. FORMAT causes the backup operation to write a new media header on all media volumes used for the backup operation. The existing contents of the volume become invalid, because any existing media header and backup sets are overwritten.

Important

Use FORMAT carefully. Formatting any volume of a media set renders the entire media set unusable. For example, if you initialize a single tape belonging to an existing striped media set, the entire media set is rendered useless.

Specifying FORMAT implies SKIP; SKIP does not need to be explicitly stated.

MEDIADESCRIPTION = { text | @text_variable }

Specifies the free-form text description, maximum of 255 characters, of the media set.

MEDIANAME = { media_name | @media_name_variable }

Specifies the media name for the entire backup media set. The media name must be no longer than 128 characters. If MEDIANAME is specified, it must match the previously specified media name already existing on the backup volumes. If it is not specified, or if the SKIP option is specified, there is no verification check of the media name.

BLOCKSIZE = { blocksize | @blocksize_variable }

Specifies the physical block size, in bytes. The supported sizes are 512, 1024, 2048, 4096, 8192, 16384, 32768, and 65536 (64 KB) bytes. The default is 65536 for tape devices and 512 otherwise. Typically, this option is unnecessary because BACKUP automatically selects a block size that is appropriate to the device. Explicitly stating a block size overrides the automatic selection of block size.

If you are taking a backup that you plan to copy onto and restore from a CD-ROM, specify BLOCKSIZE=2048.

Note

This option typically affects performance only when writing to tape devices.

Data transfer options

BUFFERCOUNT = { buffercount | @buffercount_variable }

Specifies the total number of I/O buffers to be used for the backup operation. You can specify any positive integer; however, large numbers of buffers might cause "out of memory" errors because of inadequate virtual address space in the Sqlservr.exe process.

The total space used by the buffers is determined by: BUFFERCOUNT * MAXTRANSFERSIZE.

Note

For important information about using the BUFFERCOUNT option, see the Incorrect BufferCount data transfer option can lead to OOM condition blog.

MAXTRANSFERSIZE = { maxtransfersize | @ maxtransfersize_variable }

Specifies the largest unit of transfer in bytes to be used between SQL Server and the backup media. The possible values are multiples of 65536 bytes (64 KB) ranging up to 4194304 bytes (4 MB). In a specific case of backup to URL to S3-compatible object storage, MAXTRANSFERSIZE is 10 MB. For more information, see Remarks.

When creating backups by using the SQL Writer Service, if the database has configured FILESTREAM, or includes memory optimized filegroups, then the MAXTRANSFERSIZE at the time of a restore should be greater than or equal to the MAXTRANSFERSIZE that was used when the backup was created.

For Transparent Data Encryption (TDE) enabled databases with a single data file, the default MAXTRANSFERSIZE is 65536 (64 KB). For non-TDE encrypted databases, the default MAXTRANSFERSIZE is 1048576 (1 MB) when using backup to DISK, and 65536 (64 KB) when using VDI or TAPE. For more information about using backup compression with TDE encrypted databases, see the Remarks section.

Error management options

These options allow you to determine whether backup checksums are enabled for the backup operation and whether the operation stops on encountering an error.

{ NO_CHECKSUM | CHECKSUM }

Controls whether backup checksums are enabled.

NO_CHECKSUM
Explicitly disables the generation of backup checksums (and the validation of page checksums). This is the default behavior.

CHECKSUM
Specifies that the backup operation verifies each page for checksum and torn page, if enabled and available, and generate a checksum for the entire backup.

Using backup checksums might affect workload and backup throughput.

For more information, see Possible Media Errors During Backup and Restore.

{ STOP_ON_ERROR | CONTINUE_AFTER_ERROR }

Controls whether a backup operation stops or continues after encountering a page checksum error.

STOP_ON_ERROR
Instructs BACKUP to fail if a page checksum does not verify. This is the default behavior.

CONTINUE_AFTER_ERROR
Instructs BACKUP to continue despite encountering errors such as invalid checksums or torn pages.

If you are unable to back up the tail of the log using the NO_TRUNCATE option when the database is damaged, you can attempt a tail-log log backup by specifying CONTINUE_AFTER_ERROR instead of NO_TRUNCATE.

For more information, see Possible Media Errors During Backup and Restore.

Compatibility options

RESTART

Beginning with SQL Server 2008 (10.0.x), has no effect. This option is accepted by the version for compatibility with previous versions of SQL Server.

Monitoring options

STATS [ = percentage ]

Displays a message each time another percentage completes, and is used to gauge progress. If percentage is omitted, SQL Server displays a message after each 10 percent is completed.

The STATS option reports the percentage complete as of the threshold for reporting the next interval. This is at approximately the specified percentage; for example, with STATS=10, if the amount completed is 40 percent, the option might display 43 percent. For large backup sets, this is not a problem, because the percentage complete moves very slowly between completed I/O calls.

Tape options

These options are used only for TAPE devices. If a nontape device is being used, these options are ignored.

{ REWIND | NOREWIND }

REWIND
Specifies that SQL Server releases and rewinds the tape. REWIND is the default.

NOREWIND
Specifies that SQL Server will keep the tape open after the backup operation. You can use this option to help improve performance when performing multiple backup operations to a tape.

NOREWIND implies NOUNLOAD, and these options are incompatible within a single BACKUP statement.

Note

If you use NOREWIND, the instance of SQL Server retains ownership of the tape drive until a BACKUP or RESTORE statement that is running in the same process uses either the REWIND or UNLOAD option, or the server instance is shut down. Keeping the tape open prevents other processes from accessing the tape. For information about how to display a list of open tapes and to close an open tape, see Backup Devices.

{ UNLOAD | NOUNLOAD }

Note

UNLOAD and NOUNLOAD are session settings that persist for the life of the session or until it is reset by specifying the alternative.

UNLOAD
Specifies that the tape is automatically rewound and unloaded when the backup is finished. UNLOAD is the default when a session begins.

NOUNLOAD
Specifies that after the BACKUP operation the tape remains loaded on the tape drive.

Note

For a backup to a tape backup device, the BLOCKSIZE option to affect the performance of the backup operation. This option typically affects performance only when writing to tape devices.

Log-specific options

These options are only used with BACKUP LOG.

Note

If you do not want to take log backups, use the simple recovery model. For more information, see Recovery Models.

{ NORECOVERY | STANDBY = undo_file_name }

NORECOVERY
Backs up the tail of the log and leaves the database in the RESTORING state. NORECOVERY is useful when failing over to a secondary database or when saving the tail of the log before a RESTORE operation.

To perform a best-effort log backup that skips log truncation and then take the database into the RESTORING state atomically, use the NO_TRUNCATE and NORECOVERY options together.

STANDBY = standby_file_name
Backs up the tail of the log and leaves the database in a read-only and STANDBY state. The STANDBY clause writes standby data (performing rollback, but with the option of further restores). Using the STANDBY option is equivalent to BACKUP LOG WITH NORECOVERY followed by a RESTORE WITH STANDBY.

Using standby mode requires a standby file, specified by standby_file_name, whose location is stored in the log of the database. If the specified file already exists, the Database Engine overwrites it; if the file does not exist, the Database Engine creates it. The standby file becomes part of the database.

This file holds the rolled back changes, which must be reversed if RESTORE LOG operations are to be subsequently applied. There must be enough disk space for the standby file to grow so that it can contain all the distinct pages from the database that were modified by rolling back uncommitted transactions.

NO_TRUNCATE

Specifies that the transaction log should not be not truncated and causes the Database Engine to attempt the backup regardless of the state of the database. Consequently, a backup taken with NO_TRUNCATE might have incomplete metadata. This option allows backing up the transaction log in situations where the database is damaged.

The NO_TRUNCATE option of BACKUP LOG is equivalent to specifying both COPY_ONLY and CONTINUE_AFTER_ERROR.

Without the NO_TRUNCATE option, the database must be in the ONLINE state. If the database is in the SUSPENDED state, you might be able to create a backup by specifying NO_TRUNCATE. But if the database is in the OFFLINE or EMERGENCY state, BACKUP is not allowed even with NO_TRUNCATE. For information about database states, see Database States.

About working with SQL Server backups

This section introduces the following essential backup concepts:

Backup Types Transaction Log Truncation Formatting Backup Media Working with Backup Devices and Media Sets Restoring SQL Server Backups

Note

For an introduction to backup in SQL Server, see Backup Overview.

Backup types

The supported backup types depend on the recovery model of the database, as follows

• All recovery models support full and differential backups of data.

  Scope of backup	Backup types
  Whole database	Database backups cover the whole database. Optionally, each database backup can serve as the base of a series of one or more differential database backups.
  Partial database	Partial backups cover read/-write filegroups and, possibly, one or more read-only files or filegroups. Optionally, each partial backup can serve as the base of a series of one or more differential partial backups.
  File or filegroup	File backups cover one or more files or filegroups, and are relevant only for databases that contain multiple filegroups. Under the simple recovery model, file backups are essentially restricted to read-only secondary filegroups. Optionally, each file backup can serve as the base of a series of one or more differential file backups.

• Under the full recovery model or bulk-logged recovery model, conventional backups also include sequential transaction log backups (or log backups), which are required. Each log backup covers the portion of the transaction log that was active when the backup was created, and it includes all log records not backed up in a previous log backup.

  To minimize work-loss exposure, at the cost of administrative overhead, you should schedule frequent log backups. Scheduling differential backups between full backups can reduce restore time by reducing the number of log backups you have to restore after restoring the data.

  We recommend that you put log backups on a separate volume than the database backups.

  Note

  Before you can create the first log backup, you must create a full backup.

• A copy-only backup is a special-purpose full backup or log backup that is independent of the normal sequence of conventional backups. To create a copy-only backup, specify the COPY_ONLY option in your BACKUP statement. For more information, see Copy-Only Backups.

Transaction log truncation

To avoid filling up the transaction log of a database, routine backups are essential. Under the simple recovery model, log truncation occurs automatically after you back up the database, and under the full recovery model, after you back up the transaction log. However, sometimes the truncation process can be delayed. For information about factors that can delay log truncation, see The Transaction Log.

Note

The BACKUP LOG WITH NO_LOG and WITH TRUNCATE_ONLY options have been discontinued. If you are using the full or bulk-logged recovery model recovery and you must remove the log backup chain from a database, switch to the simple recovery model. For more information, see View or Change the Recovery Model of a Database.

Formatting backup media

Backup media is formatted by a BACKUP statement if and only if any of the following is true:

• The FORMAT option is specified.
• The media is empty.
• The operation is writing a continuation tape.

Work with backup devices and media sets

Backup devices in a striped media set (a stripe set)

A stripe set is a set of disk files on which data is divided into blocks and distributed in a fixed order. The number of backup devices used in a stripe set must stay the same (unless the media is reinitialized with FORMAT).

The following example writes a backup of the AdventureWorks2022 database to a new striped media set that uses three disk files.

BACKUP DATABASE AdventureWorks2022
TO DISK = 'X:\SQLServerBackups\AdventureWorks1.bak',
DISK = 'Y:\SQLServerBackups\AdventureWorks2.bak',
DISK = 'Z:\SQLServerBackups\AdventureWorks3.bak'
WITH FORMAT,
  MEDIANAME = 'AdventureWorksStripedSet0',
  MEDIADESCRIPTION = 'Striped media set for AdventureWorks2022 database';
GO

After a backup device is defined as part of a stripe set, it cannot be used for a single-device backup unless FORMAT is specified. Similarly, a backup device that contains nonstriped backups cannot be used in a stripe set unless FORMAT is specified. To split a striped backup set, use FORMAT.

If neither MEDIANAME or MEDIADESCRIPTION is specified when a media header is written, the media header field corresponding to the blank item is empty.

Work with a mirrored media set

Typically, backups are unmirrored, and BACKUP statements simply include a TO clause. However, a total of four mirrors is possible per media set. For a mirrored media set, the backup operation writes to multiple groups of backup devices. Each group of backup devices comprises a single mirror within the mirrored media set. Every mirror must use the same quantity and type of physical backup devices, which must all have the same properties.

To back up to a mirrored media set, all of the mirrors must be present. To back up to a mirrored media set, specify the TO clause to specify the first mirror, and specify a MIRROR TO clause for each additional mirror.

For a mirrored media set, each MIRROR TO clause must list the same number and type of devices as the TO clause. The following example writes to a mirrored media set that contains two mirrors and uses three devices per mirror:

BACKUP DATABASE AdventureWorks2022
TO DISK = 'X:\SQLServerBackups\AdventureWorks1a.bak',
  DISK = 'Y:\SQLServerBackups\AdventureWorks2a.bak',
  DISK = 'Z:\SQLServerBackups\AdventureWorks3a.bak'
MIRROR TO DISK='X:\SQLServerBackups\AdventureWorks1b.bak',
  DISK = 'Y:\SQLServerBackups\AdventureWorks2b.bak',
  DISK = 'Z:\SQLServerBackups\AdventureWorks3b.bak';
GO

Important

This example is designed to allow you to test it on your local system. In practice, backing up to multiple devices on the same drive would hurt performance and would eliminate the redundancy for which mirrored media sets are designed.

Media families in mirrored media sets

Each backup device specified in the TO clause of a BACKUP statement corresponds to a media family. For example, if the TO clause lists three devices, BACKUP writes data to three media families. In a mirrored media set, every mirror must contain a copy of every media family. This is why the number of devices must be identical in every mirror.

When multiple devices are listed for each mirror, the order of the devices determines which media family is written to a particular device. For example, in each of the device lists, the second device corresponds to the second media family. For the devices in the above example, the correspondence between devices and media families is shown in the following table.

Mirror	Media family 1	Media family 2	Media family 3
0	Z:\AdventureWorks1a.bak	Z:\AdventureWorks2a.bak	Z:\AdventureWorks3a.bak
1	Z:\AdventureWorks1b.bak	Z:\AdventureWorks2b.bak	Z:\AdventureWorks3b.bak

A media family must always be backed up onto the same device within a specific mirror. Therefore, each time you use an existing media set, list the devices of each mirror in the same order as they were specified when the media set was created.

For more information about mirrored media sets, see Mirrored backup media sets. For more information about media sets and media families in general, see Media sets, media families, and backup sets.

Restore SQL Server backups

To restore a database and, optionally, recover it to bring it online, or to restore a file or filegroup, use either the Transact-SQL RESTORE statement or the SQL Server Management Studio Restore tasks. For more information, see Restore and Recovery Overview.

Additional considerations about BACKUP options

Interaction of SKIP, NOSKIP, INIT, and NOINIT

This table describes interactions between the { NOINIT | INIT } and { NOSKIP | SKIP } options.

Note

If the tape media is empty or the disk backup file does not exist, all these interactions write a media header and proceed. If the media is not empty and lacks a valid media header, these operations give feedback stating that this is not valid MTF media, and they terminate the backup operation.

Skip option	NOINIT	INIT
NOSKIP	If the volume contains a valid media header, verifies that the media name matches the given MEDIANAME, if any. If it matches, appends the backup set, preserving all existing backup sets. If the volume does not contain a valid media header, an error occurs.	If the volume contains a valid media header, performs the following checks: If MEDIANAME was specified, verifies that the given media name matches the media header's media name.1 Verifies that there are no unexpired backup sets already on the media. If there are, terminates the backup. If these checks pass, overwrites any backup sets on the media, preserving only the media header. If the volume does not contain a valid media header, generates one with using specified MEDIANAME and MEDIADESCRIPTION, if any.
SKIP	If the volume contains a valid media header, appends the backup set, preserving all existing backup sets.	If the volume contains a valid2 media header, overwrites any backup sets on the media, preserving only the media header. If the media is empty, generates a media header using the specified MEDIANAME and MEDIADESCRIPTION, if any.

¹ The user must belong to the appropriate fixed database or server roles to perform a backup operation.

² Validity includes the MTF version number and other header information. If the version specified is unsupported or an unexpected value, an error occurs.

Compatibility

Caution

Backups that are created by more recent version of SQL Server cannot be restored in earlier versions of SQL Server.

BACKUP supports the RESTART option to provide backward compatibility with earlier versions of SQL Server. But RESTART has no effect.

Remarks

Database or log backups can be appended to any disk or tape device, allowing a database and its transaction logs to be kept within one physical location.

The BACKUP statement is not allowed in an explicit or implicit transaction.

You can't back up a database in the following states:

• Restoring
• Standby
• Read only

Cross-platform backup operations, even between different processor types, can be performed as long as the collation of the database is supported by the operating system.

Starting with SQL Server 2016 (13.x), setting MAXTRANSFERSIZE larger than 65536 (64 KB) enables an optimized compression algorithm for Transparent Data Encryption (TDE) encrypted databases that first decrypts a page, compresses it, and then encrypts it again. If MAXTRANSFERSIZE is not specified, or if MAXTRANSFERSIZE = 65536 (64 KB) is used, backup compression with TDE encrypted databases directly compresses the encrypted pages, and may not yield good compression ratios. For more information, see Backup Compression for TDE-enabled Databases.

Starting with SQL Server 2019 (15.x) CU5, setting MAXTRANSFERSIZE is no longer required to enable this optimized compression algorithm with TDE. If the backup command is specified WITH COMPRESSION or the backup compression default server configuration is set to 1, MAXTRANSFERSIZE will automatically be increased to 128 K to enable the optimized algorithm. If MAXTRANSFERSIZE is specified on the backup command with a value > 64 K, the provided value is honored. In other words, SQL Server never automatically decreases the value, only increases it. If you need to back up a TDE encrypted database with MAXTRANSFERSIZE = 65536, you must specify WITH NO_COMPRESSION or ensure that the backup compression default server configuration is set to 0.

Note

There are some cases where the default MAXTRANSFERSIZE is greater than 64K:

• When the database has multiple data files created, it uses MAXTRANSFERSIZE > 64K.
• When performing backup to URL to Azure Blob Storage, the default MAXTRANSFERSIZE = 1048576 (1 MB).
• When performing backup to URL to S3-compatible object storage, the default MAXTRANSFERSIZE = 10485760 (10 MB).

Even if one of these conditions applies, you must explicitly set MAXTRANSFERSIZE greater than 64K in your backup command in order to get the optimized backup compression algorithm, unless you are on SQL Server 2019 (15.x) CU5 or later.

By default, every successful backup operation adds an entry in the SQL Server error log and in the system event log. If you back up the log very frequently, these success messages accumulate quickly, resulting in large error logs that can make finding other messages difficult. In such cases you can suppress these log entries by using trace flag 3226, if none of your automation or monitoring depends on those entries. For more information, see Trace Flags.

Interoperability

SQL Server uses an online backup process to allow a database backup while the database is still in use. During a backup, most operations are possible; for example, INSERT, UPDATE, or DELETE statements are allowed during a backup operation.

Operations that cannot run during a database or transaction log backup include:

• File management operations such as the ALTER DATABASE statement with either the ADD FILE or REMOVE FILE options.

• Shrink database or shrink file operations. This includes autoshrink operations.

If a backup operation overlaps with a file management or DBCC SHRINK operation, a conflict arises. Regardless of which of the conflicting operation began first, the second operation waits for the lock set by the first operation to time out (the time-out period is controlled by a session timeout setting). If the lock is released during the time-out period, the second operation continues. If the lock times out, the second operation fails.

Metadata

SQL Server includes the following backup history tables that track backup activity:

• backupfile
• backupfilegroup
• backupmediafamily
• backupmediaset
• backupset

When a restore is performed, if the backup set was not already recorded in the msdb database, the backup history tables might be modified.

Security

Beginning with SQL Server 2012 (11.x), the PASSWORD and MEDIAPASSWORD options are discontinued for creating backups. It is still possible to restore backups created with passwords.

Permissions

BACKUP DATABASE and BACKUP LOG permissions default to members of the sysadmin fixed server role and the db_owner and db_backupoperator fixed database roles.

Ownership and permission problems on the backup device's physical file can interfere with a backup operation. Ensure SQL Server startup account needs to have read and write permissions to the backup device and the folder where the backup files are written to. However, sp_addumpdevice, which adds an entry for a backup device in the system tables, does not check file access permissions. Such problems on the backup device's physical file might not appear until the physical resource is accessed when the backup or restore is attempted.

Examples

This section contains the following examples:

• A. Back up a complete database
• B. Back up the database and log
• C. Create a full file backup of the secondary filegroups
• D. Create a differential file backup of the secondary filegroups
• E. Create and backing up to a single-family mirrored media set
• F. Create and backing up to a multifamily mirrored media set
• G. Back up to an existing mirrored media set
• H. Create a compressed backup in a new media set
• I. Back up to Azure Blob Storage
• J. [Back up to S3-compatible object storage]((#j-backing-up-to-s3-compatible-object-storage)
• K. Track the progress of backup statement

Note

The backup how-to topics contain additional examples. For more information, see Backup Overview.

A. Back up a complete database

The following example backs up the AdventureWorks2022 database to a disk file.

BACKUP DATABASE AdventureWorks2022
 TO DISK = 'Z:\SQLServerBackups\AdvWorksData.bak'
    WITH FORMAT;
GO

B. Back up the database and log

The following example backups up the AdventureWorks2022 sample database, which uses the simple recovery model by default. To support log backups, the AdventureWorks2022 database is modified to use the full recovery model.

Next, the example uses sp_addumpdevice to create a logical backup device for backing up data, AdvWorksData, and creates another logical backup device for backing up the log, AdvWorksLog.

The example then creates a full database backup to AdvWorksData, and after a period of update activity, backs up the log to AdvWorksLog.

-- To permit log backups, before the full database backup, modify the database
-- to use the full recovery model.
USE master;
GO
ALTER DATABASE AdventureWorks2022
    SET RECOVERY FULL;
GO
-- Create AdvWorksData and AdvWorksLog logical backup devices.
USE master
GO
EXEC sp_addumpdevice 'disk', 'AdvWorksData',
'Z:\SQLServerBackups\AdvWorksData.bak';
GO
EXEC sp_addumpdevice 'disk', 'AdvWorksLog',
'X:\SQLServerBackups\AdvWorksLog.bak';
GO

-- Back up the full AdventureWorks2022 database.
BACKUP DATABASE AdventureWorks2022 TO AdvWorksData;
GO
-- Back up the AdventureWorks2022 log.
BACKUP LOG AdventureWorks2022
    TO AdvWorksLog;
GO

Note

For a production database, back up the log regularly. Log backups should be frequent enough to provide sufficient protection against data loss.

C. Create a full file backup of the secondary filegroups

The following example creates a full file backup of every file in both of the secondary filegroups.

--Back up the files in SalesGroup1:
BACKUP DATABASE Sales
    FILEGROUP = 'SalesGroup1',
    FILEGROUP = 'SalesGroup2'
    TO DISK = 'Z:\SQLServerBackups\SalesFiles.bck';
GO

D. Create a differential file backup of the secondary filegroups

The following example creates a differential file backup of every file in both of the secondary filegroups.

--Back up the files in SalesGroup1:
BACKUP DATABASE Sales
    FILEGROUP = 'SalesGroup1',
    FILEGROUP = 'SalesGroup2'
    TO DISK = 'Z:\SQLServerBackups\SalesFiles.bck'
    WITH
      DIFFERENTIAL;
GO

E. Create and backing up to a single-family mirrored media set

The following example creates a mirrored media set containing a single media family and four mirrors and backs up the AdventureWorks2022 database to them.

BACKUP DATABASE AdventureWorks2022
TO TAPE = '\\.\tape0'
MIRROR TO TAPE = '\\.\tape1'
MIRROR TO TAPE = '\\.\tape2'
MIRROR TO TAPE = '\\.\tape3'
WITH
    FORMAT,
    MEDIANAME = 'AdventureWorksSet0';

F. Create and backing up to a multifamily mirrored media set

The following example creates a mirrored media set in which each mirror consists of two media families. The example then backs up the AdventureWorks2022 database to both mirrors.

BACKUP DATABASE AdventureWorks2022
TO TAPE = '\\.\tape0', TAPE = '\\.\tape1'
MIRROR TO TAPE = '\\.\tape2', TAPE = '\\.\tape3'
WITH
    FORMAT,
    MEDIANAME = 'AdventureWorksSet1';

G. Back up to an existing mirrored media set

The following example appends a backup set to the media set created in the preceding example.

BACKUP LOG AdventureWorks2022
TO TAPE = '\\.\tape0', TAPE = '\\.\tape1'
MIRROR TO TAPE = '\\.\tape2', TAPE = '\\.\tape3'
WITH
    NOINIT,
    MEDIANAME = 'AdventureWorksSet1';

Note

NOINIT, which is the default, is shown here for clarity.

H. Create a compressed backup in a new media set

The following example formats the media, creating a new media set, and performs a compressed full backup of the AdventureWorks2022 database.

BACKUP DATABASE AdventureWorks2022 TO DISK='Z:\SQLServerBackups\AdvWorksData.bak'
WITH
    FORMAT,
    COMPRESSION;

I. Back up to Microsoft Azure Blob Storage

This example performs a full database backup of Sales to Azure Blob Storage. The storage Account name is mystorageaccount. The container is called myfirstcontainer. A stored access policy has already been created with read, write, delete, and list rights. The SQL Server credential, https://mystorageaccount.blob.core.windows.net/myfirstcontainer, was created using a Shared Access Signature that is associated with the Stored Access Policy. For information on SQL Server backup to Azure Blob Storage, see SQL Server Backup and Restore with Azure Blob Storage and SQL Server Backup to URL.

BACKUP DATABASE Sales
TO URL = 'https://mystorageaccount.blob.core.windows.net/myfirstcontainer/Sales.bak'
WITH STATS = 5;

You can also back up your database into multiple stripes, and it would look like this:

BACKUP DATABASE Sales
TO URL = 'https://mystorageaccount.blob.core.windows.net/myfirstcontainer/Sales-01.bak',
URL = 'https://mystorageaccount.blob.core.windows.net/myfirstcontainer/Sales-02.bak',
URL = 'https://mystorageaccount.blob.core.windows.net/myfirstcontainer/Sales-03.bak',
URL = 'https://mystorageaccount.blob.core.windows.net/myfirstcontainer/Sales-04.bak'
WITH COPY_ONLY;

J. Back up to S3-compatible object storage

Applies to: SQL Server 2022 (16.x)

This example performs a full backup database of the Sales database to S3-compatible object storage platform. The name of the credential is not required in the statement or to match the exact URL path, but will perform a lookup for the proper credential on the URL provided. For more information, see SQL Server backup and restore with S3-compatible object storage.

BACKUP DATABASE Sales
TO      URL = 's3://10.10.10.10:8787/sqls3backups/sales_01.bak'
,       URL = 's3://10.10.10.10:8787/sqls3backups/sales_02.bak'
,       URL = 's3://10.10.10.10:8787/sqls3backups/sales_03.bak'
WITH    FORMAT
,       STATS               = 10
,       COMPRESSION;

K. Track the progress of backup statement

The following query returns information about the currently running backup statements:

SELECT query = a.text, start_time, percent_complete,
    eta = dateadd(second,estimated_completion_time/1000, getdate())
FROM sys.dm_exec_requests r
    CROSS APPLY sys.dm_exec_sql_text(r.sql_handle) a
WHERE r.command LIKE 'BACKUP%';

Related content

• Backup Devices
• Media Sets, Media Families, and Backup Sets
• Tail-Log Backups
• ALTER DATABASE
• DBCC SQLPERF
• RESTORE
• RESTORE FILELISTONLY
• RESTORE HEADERONLY
• RESTORE LABELONLY
• RESTORE VERIFYONLY
• sp_addumpdevice
• sp_configure
• sp_helpfile
• sp_helpfilegroup
• Server Configuration Options
• Piecemeal Restore of Databases With Memory-Optimized Tables