Understanding and Resolving the ORA-01115 Error in Oracle Databases

Error Description

  • ORA-01115: “IO error reading block from file %s (block # %s)”
  • Cause: The device on which the file resides is likely offline.
  • Action: Restore access to the device.

Common Issues Accompanying ORA-01115

  • Often accompanied by an ORA-01110 error.
  • May include an OS-level Oracle error message, like ORA-0737X.
  • OS errors (e.g., Error # 5 in Unix) may also occur.

Solution Approach

  1. Hardware Issues: ORA-01115 is mostly caused by hardware problems. Isolating hardware issues is crucial before attempting database-level solutions.
  2. Hardware Checks: Run OS-level tools and diagnostics for disks, controllers, and I/O subsystems. Pay special attention to the disk where the referenced data file resides.
  3. Diagnosing Unknown Issues:
    • Estimate the cause and scope of the problem.
    • Check the instance’s alert.log file for other ORA-01115 entries.
    • Determine if the issues are related to controller problems, disk issues, or specific data file corruption.

Steps for Resolving the Error

  1. For Unknown Issues:
    • Close the database if the data file is in the SYSTEM tablespace or if the database is in NOARCHIVELOG mode.
    • If the database is in ARCHIVELOG mode, try to close it; if not possible, take the affected data file offline.
    • Attempt to copy the data file to a different disk.
    • If copy fails, assume data file loss and proceed based on the tablespace type.
  2. For Known Issues:
    • Controller Issues: Often intermittent and do not usually damage data files. Try copying affected files to a different disk.
    • Disk Issues: Move data files from the faulty disk to a different one.
    • Data Block Corruption: Consider the file lost if it belongs to SYSTEM, ROLLBACK, or READ-ONLY tablespaces.
    • Large File Issues on Solaris: For Oracle versions 7.1.4 or lower, large files (>2GB) may cause errors.
  3. After Resolving Issues:
    • Rename and recover the successfully copied data file in Oracle.
    • Open the database and perform media recovery on the file if it was taken offline.


ORA-01115 error signifies an IO error when reading a block from a file in Oracle databases. It is primarily related to hardware issues or data block corruption. Diagnosing the root cause is crucial before attempting any recovery. Depending on whether the cause is known or unknown, different steps should be followed, always prioritizing hardware checks and ensuring data file integrity post-recovery.


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