SQL Server Error 823

Error number

823

Severity

24 (fatal: the connection ends; may indicate a serious problem)

State

2

Product

Microsoft SQL Server Database Engine

Versions

All supported SQL Server versions (2016 to 2025), Azure SQL Managed Instance

Category

Corruption & Consistency

Last reviewed

23 October 2026

What it means

Error 823 means Windows itself reported that a read or write of a database file failed, so SQL Server could not get or save the page; the cause is in the disk, controller, driver or network path to the storage.

SQL Server reads and writes database files through Windows file APIs. When one of those calls fails with an operating system error, SQL Server raises 823 at severity 24 (a hardware or media error): the statement fails and the connection is closed. For reads, Microsoft documents that SQL Server retries four times before giving up; if a retry succeeds, the query carries on and error 825 is written to the error log as a warning instead.

The message tells you where to look: the operating system error in brackets (for example 1117, an I/O device error, or 21, device not ready), whether it was a read or a write, the file, and the byte offset. Dividing the offset by 8,192 gives the page number. Unlike error 824, where Windows reported success but the page content was wrong, 823 means the I/O itself failed.

Common causes

• A failing disk, controller, HBA or storage array, or outdated firmware.
• A faulty or outdated storage driver, multipath software or virtual disk driver.
• A volume or LUN that went offline, or an unstable network path to SAN or NAS storage (OS error 21 means the device is not ready).
• Filter drivers in the I/O path, such as antivirus or backup agents, interfering with database files.
• File system inconsistencies on the volume that holds the database files.

Diagnose it

Read-only These queries only read metadata and dynamic management views. They do not change data, permissions or configuration, so they are safe to run first.

SELECT DB_NAME(database_id) AS database_name, file_id, page_id,
       event_type, error_count, last_update_date
FROM msdb.dbo.suspect_pages
ORDER BY last_update_date DESC;

EXEC sp_readerrorlog 0, 1, N'The operating system returned error';
EXEC sp_readerrorlog 0, 1, N'succeeded after failing';

SELECT DB_NAME(mf.database_id) AS database_name, mf.physical_name,
       vs.volume_mount_point, vs.logical_volume_name
FROM sys.master_files AS mf
CROSS APPLY sys.dm_os_volume_stats(mf.database_id, mf.file_id) AS vs
ORDER BY vs.volume_mount_point, database_name;

DBCC CHECKDB (N'AppDb') WITH NO_INFOMSGS, ALL_ERRORMSGS;

How to fix it

Each fix is labelled with what it changes. Try read-only checks and the least invasive fix first, and test changes outside production.

RESTORE DATABASE AppDb
FROM DISK = N'D:\Backups\AppDb_full.bak'
WITH NORECOVERY, REPLACE,
     MOVE N'AppDb' TO N'F:\SqlData\AppDb.mdf',
     MOVE N'AppDb_log' TO N'F:\SqlLogs\AppDb_log.ldf';
-- then RESTORE LOG ... WITH NORECOVERY for each log backup, finishing WITH RECOVERY

EXEC msdb.dbo.sp_add_alert @name = N'Error 823 I/O failure', @message_id = 823, @severity = 0, @include_event_description_in = 1;
EXEC msdb.dbo.sp_add_alert @name = N'Error 824 page check failure', @message_id = 824, @severity = 0, @include_event_description_in = 1;
EXEC msdb.dbo.sp_add_alert @name = N'Error 825 read retry', @message_id = 825, @severity = 0, @include_event_description_in = 1;

Examples

A read fails on a failing disk

Shown as documented by Microsoft; not reproduced here because it needs a failing disk or I/O path. The query fails and the connection is closed. The same message is written to the error log as Error: 823, Severity: 24, State: 2.

SELECT * FROM dbo.Orders;

Msg 823, Level 24, State 2, Line 1
The operating system returned error 1117(The request could not be performed because of an I/O device error.) to SQL Server during a read at offset 0x0000002d460000 in file 'E:\SqlData\AppDb.mdf'. Additional messages in the SQL Server error log and operating system error log may provide more detail. This is a severe system-level error condition that threatens database integrity and must be corrected immediately. Complete a full database consistency check (DBCC CHECKDB). This error can be caused by many factors; for more information, see SQL Server Books Online.

How to prevent it

Treat error 825 as the early warning it is: alert on 823, 824 and 825 with SQL Server Agent alerts, and investigate the storage as soon as 825 appears rather than waiting for reads to fail outright.

Keep storage firmware and drivers current, exclude database files from antivirus scanning, run DBCC CHECKDB regularly and test restores, so an I/O failure ends in a planned restore rather than data loss.

Common questions

Learn more on CodeWithSQL

• Working with large databases

Official documentation

• MSSQLSERVER_823 (Microsoft Learn)
• Manage the suspect_pages table
• Restore pages (SQL Server)
• DBCC CHECKDB (Transact-SQL)

Last technically reviewed 23 October 2026; examples and diagnostics run on SQL Server 2025 (17.0.1145.4). Message text checked against the engine's sys.messages catalogue.