SQL Server Error 823 — The operating system returned an error during I/O
The operating system returned error 'X' to SQL Server during a read/write at offset Y in file 'Z'.
This is severity 24 — a serious error. Unlike a logical bug in your code, this means the operating system or storage layer itself reported a failure while SQL Server tried to read or write a page. It's a signal to investigate hardware/storage, not your query.
Common causes
- Failing or degraded physical disk / storage array
- Storage controller, driver, or firmware issues
- SAN or network-attached storage connectivity problems
- Antivirus real-time scanning interfering with SQL Server's data/log files
- Misconfigured storage (unsupported caching, incorrect sector alignment) especially on virtualized or cloud storage
How to fix it
- Run DBCC CHECKDB immediately to assess whether any actual data corruption resulted from the I/O failure.
- Check the Windows System and Application event logs around the same timestamp for related disk/storage hardware errors.
- Check storage health directly — SMART data for local disks, or your SAN/cloud provider's health dashboard.
- Confirm antivirus is configured to exclude SQL Server data, log, and backup file paths.
- If corruption is confirmed, restore from a known-good backup rather than continuing to write to a failing volume — engage your storage team/vendor in parallel.
Paste your error and DBCC CHECKDB output here for help interpreting the scope of the issue.
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