Article ID: 926930 - Last Review: April 24, 2012 - Revision: 2.0

Hard disk drive sector-size support boundaries in SQL Server

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INTRODUCTION

Microsoft SQL Server currently supports the following sector sizes that are equal to or less than 4 kilobytes (KB):

Physical sector sizes that evenly divide into 4 KB
Physical sector sizes that are smaller than the size of the original formatted sector size of the database, as long as the smaller sector size is evenly divisible into the originally formatted sector size
512 bytes
1,024 bytes
2,048 bytes
4,096 bytes

Note Microsoft SQL Server supports disk drives that have standard native sector sizes of 512 bytes and 4 KB.

SQL Server requires correct reporting of physical sector size to maintain data safety and avoid data loss. Avoidance of sector rewrites is a fundamental requirement of SQL Server. We do not support the read, write, and modify behavior that logical sector size reporting causes.

For more information about support for larger sector sizes, see the "4-KB disk sector sizes" section in the following white paper:

http://technet.microsoft.com/en-us/library/cc917726.aspx (http://technet.microsoft.com/en-us/library/cc917726.aspx)

If you are using Advanced Format Disks that are physically formatted with 4,096 bytes, but expose a logical sector size of 512 bytes, then you must update your SQL Server systems with the following fixes to be in a supported state:

Windows Update to enable correct recognition and reporting of physical and logical sector size:
- 2553708 (http://support.microsoft.com/kb/2553708/en-us/ ) A hotfix rollup that improves Windows Vista and Windows Server 2008 compatibility with Advanced Format disks
- 982018 (http://support.microsoft.com/kb/982018/en-us/ ) An update that improves the compatibility of Windows 7 and Windows Server 2008 R2 with Advanced Format Disks is available
SQL Updates to use the updated logical and physical sector sizes in the SQL Server transaction log manager:
- SQL Server 2008 R2 Service Pack 1 and later versions of SQL Server 2008 R2
- SQL Server 2012 RTM and later versions of SQL Server 2012

The disk drive manufacturer specification should indicate whether the drive is an Advanced Format Disk. After you apply the Windows updates, utilities such as fsutil start reporting both the physical and logical sector sizes. If you use Advanced Format Disks without the updates that are mentioned earlier in this section, there is a risk of potential data loss and performance issues. This is because the drive firmware has to perform Read-Modify-Write to support the logical 512-byte and physical 4,096-byte sector mappings. For more information about this behavior, visit the following MSDN website:

http://blogs.msdn.com/b/psssql/archive/2011/01/13/sql-server-new-drives-use-4k-sector-size.aspx (http://blogs.msdn.com/b/psssql/archive/2011/01/13/sql-server-new-drives-use-4k-sector-size.aspx)

Note Disk drives that have native 4KB sector size (both physical and logical) will work fine without the Windows and SQL updates that are mentioned earlier in this section.