Wait Type PREEMPTIVE_OS_BACKUPREAD

Wait statistics, in the context of SQL Server, refer to the amount of time that a query spends waiting to access data in the database. When a client application requests data from the database, the request is placed in a queue and the client application must wait for its turn to access the data. The time that the query spends waiting is called a "wait" and is tracked by SQL Server. This information can be used to identify potential performance bottlenecks and optimize the performance of the database. Wait statistics are commonly used by database administrators to diagnose and troubleshoot performance issues in SQL Server.

What Is the PREEMPTIVE_OS_BACKUPREAD Wait Type?

The PREEMPTIVE_OS_BACKUPREAD wait type occurs when SQL Server is waiting on the operating system to read data needed for a backup. Normally, SQL Server operates in "cooperative mode," meaning it can manage its own resources and schedule processes. But when SQL Server needs help from the operating system (like reading data from disk during a backup), it switches to a "preemptive" mode.

In preemptive mode, SQL Server hands over control to the OS to complete certain tasks. PREEMPTIVE_OS_BACKUPREAD is one such preemptive wait type, meaning SQL Server is temporarily waiting for the OS to handle reading data for a backup operation.

When Does PREEMPTIVE_OS_BACKUPREAD Appear?

This wait type generally appears during the backup process when SQL Server needs to read from a source file or disk. It can also happen during certain restore operations, especially if SQL Server is reading large files or working with slower storage media.

Common scenarios include:

• Full database backups – SQL Server is reading from data files to create a backup.
• Differential or log backups – SQL Server is reading transaction logs or modified pages.
• Restore operations – SQL Server may also encounter this wait when restoring a database and reading from backup files.

If you see this wait type frequently, it may indicate that something in the backup read process is slower than expected.

Why PREEMPTIVE_OS_BACKUPREAD Matters

Frequent or prolonged PREEMPTIVE_OS_BACKUPREAD waits could signal potential issues with your backup process or the underlying storage. For instance, if backups are reading from a slow disk, or if there’s a bottleneck in the I/O subsystem, you might see this wait type more often.

To troubleshoot:

• Check your storage performance. Look for signs of I/O bottlenecks, especially on disks used for backups.
• Consider using faster storage media if possible, as this may help reduce read times during backups.
• Review your backup schedule and load to ensure you’re not overloading the disk with multiple concurrent backups.

Identifying and optimizing issues related to PREEMPTIVE_OS_BACKUPREAD can help improve your overall backup performance, ensuring SQL Server continues running smoothly.

Conclusion

The PREEMPTIVE_OS_BACKUPREAD wait type may seem complex, but it simply means SQL Server is waiting on the operating system to handle reading data for a backup. By monitoring this wait type and optimizing storage and backup processes, you can help minimize the impact on your SQL Server's performance.

For more information on SQL Server performance tuning and managed services, Stedman Solutions offers specialized SQL Server support, including monitoring, backup optimization, and continuous performance management.

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Applies to

Related Waits

See Also

• More About PREEMPTIVE_OS_BACKUPREAD