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How to Detect and Fix a Corruption in the Datafile OS Header/Block Zero - ORA-27047 DBV-107 ORA-1157/ORA-27048 (Doc ID 360032.1)

Last updated on JANUARY 31, 2022

Applies to:

Oracle Database - Enterprise Edition - Version to [Release 8.0.5 to 12.1]
Oracle Database Cloud Schema Service - Version N/A and later
Oracle Database Exadata Cloud Machine - Version N/A and later
Oracle Cloud Infrastructure - Database Service - Version N/A and later
Oracle Database Cloud Exadata Service - Version N/A and later
Information in this document applies to any platform.


OS block in an Oracle file

  • The OS Block Header is in the first datafile block. It is used by Oracle to store Operating System information.
  • It is the Block Zero. It is not the datafile header which is in Oracle Block 1.
  • Corruption in Block Zero will not cause damage to the data and in versions lower than 11g it is not detected by dbverify/rman.  In 11g Dbverify has been enhanced to detect it.
  • dbfsize can be used to check the consistency of Block 0.
  • When this block is corrupted the database may sometimes be opened with no errors as Block 0 is only checked by some specific database operations like 'CREATE CONTROLFILE' or in 11g during Database OPEN.


  • Creating the control file may report error ORA-27047 when OS block header is invalid for a particular datafile:
ORA-27047 : unable to read the header block of file.
Example taken from HPUX:





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 OS block in an Oracle file

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