SQL Server Database Engine Disk Input/Output (I/O) requirements

This article describes the SQL Server Database Engine Disk Input/Output (I/O) requirements.

Original product version:   SQL Server
Original KB number:   967576


SQL Server requires that systems support guaranteed delivery to stable media, as outlined in the following download documents:

This requirement includes, but is not limited to, the following conditions:

  • Windows logo certification
  • Write ordering
  • Caching stability
  • No data rewrites

Systems that meet these requirements support SQL Server database storage. Systems do not have to be listed on SQL Server storage solutions programs, but they must guarantee that the requirements are met.

SQL Server maintains the atomicity, consistency, isolation, and durability (ACID) property by using the Write-Ahead Logging (WAL) protocol.


The incorrect use of SQL Server with an improperly tested solution may result in data loss, including total database loss.

Technical support

Microsoft will provide full support for SQL Server and SQL Server-based applications. However, issues that are caused by the I/O solution will be referred to the device manufacturer. Symptoms may include, but are not limited to, the following:

  • Database corruption
  • Backup corruption
  • Unexpected data loss
  • Missing transactions
  • Unexpected I/O performance variances

To determine whether your hardware solution supports "guaranteed delivery to stable media" as outlined under the SQL Server Always-On program, check with your vendor. We also recommend that you contact your vendor to verify that you have correctly deployed and configured the solution for transactional database use.

It is a common troubleshooting practice for a Microsoft Support professional to ask you to disable nonessential jobs and to disable or remove third-party components, move database files, uninstall drivers, and perform similar actions. We always try to reduce the scope of the issue while we work to identify it. After an issue is identified as unrelated to the jobs or third-party products, those jobs or third-party products may be reintroduced to production.

For more information, see the following article:

More information

The following table provides links to additional information that is related to specific I/O configurations.

SQL Server I/O Internals
File System Features
  • SQL Server databases not supported on compressed volumes (except 2005 read-only files)
  • Decreased performance in some features of SQL Server when you use EFS to encrypt database files
I/O caching
Physical layout and design
Xperf resources:
NAS (Network Attached Storage) Description of support for network database files in SQL Server
iSCSI Support for SQL Server on iSCSI technology components
Mirroring and Always On availability groups These white papers also apply to Microsoft SQL Server 2008 and later versions of SQL Server.
I/O affinity INF: Understanding How to Set the SQL Server I/O Affinity Option