Recover Corrupted Datafile Without RMAN Backup

How to Recover Corrupted Datafile Without Rman backup in Oracle database

1. “There may be a situation where a sensitive
database gets us into trouble due to disk block
corruption or lack of a recoverable backup.

That is why as a database administrator, it is at the
forefront of all tasks to ensure that the backup is
correct and usable.

Alireza Kamrani
03/March/2025

44 So, if this critical situation occurs and we do
not have a backup, what methods do you know?
These are sometimes cases for which some People
demand a lot of money from the companies
involved in the problem.

Despite how effective these methods can be useful
in retrieving healthy data in critical situations,
Today, | want to mention a few of these techniques.
In fact, suppose that due to lack of backup, we are
looking for a tool that can recover at least part of
our data.

2. #20n Linux systems, there are tools and methods
that can help read Oracle datafiles and attempt to
recover healthy blocks into a new datafile without
relying on RMAN. These methods usually involve
working at the raw file system level to extract the
available data, bypassing the Oracle database's
normal recovery mechanisms.

Here are some Linux-based tools and techniques
that can help you achieve this:

1. Use PRM-DUL (Data Unloader)

As previously mentioned, PRM-DUL (Data Unloader)
is a tool specifically designed to extract data from
Oracle datafiles, even if the Oracle instance cannot
be started or if a datafile is corrupted.

e How it works: PRM-DUL reads Oracle's raw
database files (i.e., .dbf files) and attempts to

3. extract all healthy blocks, skipping over
corrupted ones.

e Key Features:
e Works without RMAN backups.
e Can handle corrupted or missing datafiles.

e Supports extraction of data from raw Oracle
database files.

e Works on Linux and other platforms.
e Usage: You would point the tool to your Oracle
datafiles, and it would attempt to recover

healthy blocks and write them to a new file.

Official Website: PRM-DUL

2. Use dd Command for Raw Data
Access (Manual Method)

On Linux, you can use the dd command to perform
low-level operations on raw datafiles. This

4. command can be helpful when you want to copy
Oracle datafiles block-by-block, and it may allow you
to isolate healthy blocks from a corrupted datafile.

e How it works: The dd command copies raw
bytes from one file to another. You can use this
to copy a corrupted .dbf file to a new file,
potentially skipping the corrupted blocks
manually by using block offsets and seeking
specific areas of the file.

Example usage:

dd if=/path_to_corrupted_datafile of=/
path_to_new_datafile bs=8192 seek=0 count=1000

e ¡f=: Input file (source corrupted datafile).

e of=: Output file (destination where healthy
blocks will be copied).

e bs=: Block size (typically 8192 bytes for Oracle
datafiles).

e seek=: Specifies the number of blocks to skip in

5. the output file.
e count=: Specifies the number of blocks to copy.

You can use this technique to copy blocks manually
from the corrupted datafile into a new one. It's a bit
rudimentary and requires identifying which blocks
are healthy, but it may help extract usable data.

3. Use hexedit or xxd to Inspect
Datafiles

If you suspect that the corruption is localized to
specific sections of the datafile and you want to
inspect the raw contents, you can use tools like
hexedit or xxd to view the datafile in hexadecimal
format.

e hexedit: A simple hex editor to view the
contents of binary files.

6. hexedit /path_to_datafile
e xxd: A command-line hex dump utility.
xxd /path_to_datafile

You can search through the raw data in the file to
see where the corruption might be and manually
extract the healthy blocks. This is a tedious and
difficult process, but it can sometimes help identify
healthy data in an otherwise corrupt file.

4. Manual Recovery with Oracle Tools
(DBMS_REPAIR, Offline Recovery)

While you may not be using RMAN, Oracle's
DBMS_REPAIR package can help identify and
manage corrupted objects at the block level. You
can mark corrupt blocks as "bad" and work with
Oracle to extract the rest of the data.

e Steps:

e Identify the corrupt blocks using the
DBMS_REPAIR package.

7. e Mark corrupt objects or blocks so Oracle avoids
them.

e Extract healthy data using traditional export/
import methods or Data Pump.

e Optionally, recreate the tablespace or restore
the tables if the corruption is localized.

This requires that the Oracle instance is still running
and accessible, but it allows you to bypass the
corrupted parts and extract healthy data.

5. Oracle Datafile Recovery with dbv
(Database Verification)

Oracle provides the DBV (Database Verification)
utility, which can be used to scan datafiles for
corruption. This tool does not perform recovery but

8. can help identify blocks that are corrupt.
e How to use it: dbv FILE=/path_to_datafile

While DBV does not perform recovery, it can give
you detailed information about the extent of
corruption and identify corrupt blocks, which may
help in manual recovery processes (like using dd or
PRM-DUL).

6. Use Third-Party Tools (e.g., Stellar
Repair for Oracle)

There are several third-party tools that can scan
corrupted Oracle datafiles and attempt to recover
the healthy blocks into new datafiles. These tools
typically work by reading the raw Oracle datafiles
and bypassing the corrupted blocks, much like PRM-
DUL.

e Stellar Repair for Oracle: A tool that can repair
corrupted datafiles and export the healthy
blocks to new files. It provides an easy-to-use
interface and automated recovery.

9. e DataNumen Oracle Recovery: Another third-
party tool that supports recovery of corrupted
or deleted datafiles.

These tools often work by extracting valid blocks
and creating new datafiles for Oracle, making them
an excellent option when RMAN backups are not
available.

7. Using Oracle SQL*Plus to Perform
Recovery (If Applicable)

If the datafile is not completely lost and the
corruption is minor, SQL*Plus can be used to
perform basic recovery by clearing corrupted
segments or tablespaces. If the corruption is
isolated to specific tables, you can drop and
recreate them, then reimport data if necessary.

8. Use Oracle Flashback Technology (If
Enabled)

If Oracle Flashback is enabled on your database,
you may be able to flashback to a point in time

10. before the corruption occurred, recovering the
datafile to an earlier state. This may not recover the
deleted or corrupted blocks but can help if the
corruption was recent.

FLASHBACK DATABASE TO SCN <scn_number>;

Flashback allows you to restore the database to a
state where the datafile was not corrupted, although
it may not help with block-level corruption.

Summary

While RMAN is the typical solution for datafile
corruption recovery, here are some Linux tools and
methods that can help recover healthy blocks from
Oracle datafiles without RMAN:

e PRM-DUL (Data Unloader) - A third-party tool
that can extract healthy data from corrupted or

11. deleted Oracle datafiles.

dd Command - Low-level data copying tool that
can be used to manually recover healthy blocks
from corrupted datafiles.

hexedit / xxd - Hex editors that can be used to
inspect raw datafile contents for manual block
recovery.

DBMS_REPAIR - Oracle's built-in tool for
managing corrupted objects and blocks within a
database.

dbv (Database Verification) - Oracle tool for
identifying corrupt blocks in datafiles.

Third-Party Tools - Tools like Stellar Repair for
Oracle or DataNumen Oracle Recovery that can
automatically recover healthy blocks into new
files.

Oracle Flashback - If enabled, Flashback can
help restore the database to a prior point in time
before the corruption occurred.

12. Each of these methods requires specific technical
expertise and tools, so the approach will depend on
the level of corruption and available resources.

i And of course, | don't need to say that having
multiple backups in safe locations, as well as
maintaining log archives after each backup and
using Rman, is the best and most useful method for
recovery in critical situations. «Ea

DATABASE BOX

Alireza Kamrani