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database-instant-file-initialization.md

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title description author ms.author ms.reviewer ms.date ms.service ms.subservice ms.topic helpviewer_keywords
Database Instant File Initialization
Learn about instant file initialization and how to enable it on your database. Instant file initialization (IFI) allows for faster file operations.
WilliamDAssafMSFT
wiassaf
randolphwest
02/19/2025
sql
configuration
conceptual
initializing files [SQL Server]
instant file initialization [SQL Server]
fast file initialization [SQL Server]
file initialization [SQL Server]
IFI [SQL Server]
database instant file initialization [SQL Server]

Database instant file initialization

[!INCLUDE SQL Server]

In this article, you learn about instant file initialization (IFI) and how to enable it to speed up growth for your [!INCLUDE ssnoversion-md] database files.

By default, data and log files are initialized to overwrite any existing data left on the disk from previously deleted files. Data and log files are first initialized by zeroing the files (filling with zeros) when you perform the following operations:

  • Create a database.
  • Add data or log files, to an existing database.
  • Increase the size of an existing file (including autogrow operations).
  • Restore a database or filegroup.

In [!INCLUDE ssNoVersion], instant file initialization allows for faster execution of the previously mentioned file operations, since it reclaims used disk space without filling that space with zeros. Instead, disk content is overwritten as new data is written to the files.

In [!INCLUDE ssazure-sqldb] and [!INCLUDE ssazuremi-md], instant file initialization is available for transaction log files only.

Instant file initialization and the transaction log

Applies to: [!INCLUDE sssql22-md] and later versions, and [!INCLUDE ssazure-sqldb] and [!INCLUDE ssazuremi-md].

Historically, transaction log files couldn't be initialized instantaneously. However, starting with [!INCLUDE sssql22-md] (all editions) and in [!INCLUDE ssazure-sqldb] and [!INCLUDE ssazuremi-md], transaction log autogrowth events up to 64 MB can benefit from instant file initialization. The default auto growth size increment for new databases is 64 MB. Transaction log file autogrowth events larger than 64 MB can't benefit from instant file initialization.

Unlike instant file initialization for data files, which is prevented if transparent data encryption (TDE) is enabled, instant file initialization is allowed for transaction log growth on databases that have TDE enabled, because of how the transaction log file grows, and the fact that the transaction log is written into in a serial fashion.

  • Instant file initialization is in use for General Purpose and Business Critical tiers of [!INCLUDE ssazure-sqldb], and [!INCLUDE ssazuremi-md], only to benefit the growth of transaction log files.

  • Instant file initialization isn't configurable in [!INCLUDE ssazure-sqldb] and [!INCLUDE ssazuremi-md].

Enable instant file initialization

Instant file initialization of data files is only available if the [!INCLUDE ssNoVersion] service startup account is granted SE_MANAGE_VOLUME_NAME. Members of the Windows Administrator group have this right and can grant it to other users by adding them to the Perform Volume Maintenance Tasks security policy. The SE_MANAGE_VOLUME_NAME right isn't required for instant file initialization of growth events up to 64 MB in the transaction log, which was introduced with the release of [!INCLUDE sssql22-md].

Important

Some feature usage, such as Transparent data encryption (TDE), can prevent instant file initialization (IFI). In [!INCLUDE sssql22-md] and later versions, and on [!INCLUDE ssazure-sqldb] and [!INCLUDE ssazuremi-md], IFI is allowed on the transaction log. For more information, see Instant file initialization and the transaction log.

In [!INCLUDE sssql16-md] and later versions, this permission can be granted to the service account at install time, during setup.

If you use the command prompt install, add the /SQLSVCINSTANTFILEINIT argument, or check the box Grant Perform Volume Maintenance Task privilege to SQL Server Database Engine Service in the installation wizard.

To grant an account the Perform volume maintenance tasks permission:

  1. On the computer where the data file will be created, open the Local Security Policy application (secpol.msc).

  2. In the left pane, expand Local Policies, and then select User Rights Assignment.

  3. In the right pane, double-click Perform volume maintenance tasks.

  4. Select Add User or Group and add the [!INCLUDE ssnoversion-md] service account.

  5. Select Apply, and then close all Local Security Policy dialog boxes.

  6. Restart the [!INCLUDE ssnoversion-md] service.

  7. Check the [!INCLUDE ssNoVersion] error log at startup.

    Applies to: [!INCLUDE ssNoVersion] (Starting with [!INCLUDE ssSQL11] SP4, [!INCLUDE ssSQL14] SP2, and [!INCLUDE sssql16-md] and later).

    1. If the [!INCLUDE ssNoVersion] service startup account is granted SE_MANAGE_VOLUME_NAME, an informational message that resembles the following example is logged:

      Database Instant File Initialization: enabled. For security and performance considerations see the topic 'Database Instant File Initialization' in SQL Server Books Online. This is an informational message only. No user action is required.

    2. If the [!INCLUDE ssNoVersion] service startup account was not granted SE_MANAGE_VOLUME_NAME, an informational message that resembles the following example is logged:

      Database Instant File Initialization: disabled. For security and performance considerations see the topic 'Database Instant File Initialization' in SQL Server Books Online. This is an informational message only. No user action is required.

    [!NOTE]
    In [!INCLUDE ssnoversion-md], use the value of instant_file_initialization_enabled in the sys.dm_server_services dynamic management view to identify if instant file initialization is enabled for your instance.

Security considerations

We recommend enabling instant file initialization as the benefits can outweigh the security risk.

When you use instant file initialization, the deleted disk content is overwritten only as new data is written to the files. For this reason, the deleted content is potentially accessible by an unauthorized principal, until some other data writes on that specific area of the data file.

While the database file is attached to the instance of [!INCLUDE ssNoVersion], this information disclosure risk is reduced by the discretionary access control list (DACL) on the file. This DACL allows file access only to the [!INCLUDE ssNoVersion] service account and the local administrator. However, when the file is detached, it's potentially accessible by a user or service that doesn't have SE_MANAGE_VOLUME_NAME.

Similar considerations exist when:

  • The database is backed up. If the backup file isn't protected with an appropriate DACL, the deleted content can become available to an unauthorized user or service.

  • A file is grown using IFI. A [!INCLUDE ssnoversion-md] administrator could potentially access the raw page contents and see the previously deleted content.

  • The database files are hosted on a storage area network. It's also possible that the storage area network always presents new pages as preinitialized, and having the operating system reinitialize the pages might be unnecessary overhead.

If the potential for disclosing deleted content is a concern, you should take one or both of the following actions:

  • Always make sure that any detached data files and backup files have restrictive DACLs.

  • Disable instant file initialization for the instance of [!INCLUDE ssNoVersion]. To do so, revoke SE_MANAGE_VOLUME_NAME from the [!INCLUDE ssNoVersion] service startup account.

    [!NOTE]
    Disabling will increase allocation times for data files, and only affects files that are created or increased in size after the user right is revoked.

SE_MANAGE_VOLUME_NAME user right

The SE_MANAGE_VOLUME_NAME user privilege can be assigned in Windows Administrative Tools, Local Security Policy applet. Under Local Policies select User Right Assignment and modify the Perform volume maintenance tasks property.

Performance considerations

The Database File initialization process writes zeros to the new regions of the file under initialization. The duration of this process depends on size of file portion that is initialized and on the response time and capacity of the storage system. If the initialization takes a long time, you might see the following messages recorded in the [!INCLUDE ssnoversion-md] error log and the Application Log.

Msg 5144
Autogrow of file '%.*ls' in database '%.*ls' was cancelled by user or timed out after %d milliseconds. Use ALTER DATABASE to set a smaller FILEGROWTH value for this file or to explicitly set a new file size.

Msg 5145
Autogrow of file '%.*ls' in database '%.*ls' took %d milliseconds. Consider using ALTER DATABASE to set a smaller FILEGROWTH for this file.

A long autogrow of a database and/or transaction log file can cause query performance problems. An operation that requires the autogrowth of a file holds on to resources such as locks or latches during the duration of the file grow operation. You might see long waits on latches for allocation pages. The operation that requires the long autogrow shows a wait type of PREEMPTIVE_OS_WRITEFILEGATHER.

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