605: Attempt to fetch logical page belongs to a different allocation unit
SQL ServerWhat does it mean?
While reading a page, SQL Server found a page belonging to a different object rather than the expected object/allocation unit. This is a strong indicator of serious physical/logical database corruption.
Why does it happen?
Broken page linkage caused by storage/disk failure, a controller or driver bug, write cache corruption during a sudden power loss, or file system damage. A 'transient 605' can occasionally stem from temporary I/O issues, but persistent ones are real corruption.
How to fix it
Immediately run DBCC CHECKDB ('mydb') WITH NO_INFOMSGS, ALL_ERRORMSGS to determine the extent of the damage. If possible, restore from a known-good backup (PITR that minimizes data loss is preferred). Test the storage/hardware and verify the PAGE_VERIFY CHECKSUM setting. REPAIR options can cause data loss, so use them only as a last resort and after taking a backup; in critical environments, engage Microsoft support.
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