Experiences with Oracle DUL

Yesterday I had my first experience with Oracle DUL.

A customer had major disk damages on his RAID 5 system, but the backups he made daily were (sadly) never tested (lesson!). Recovery gave lots off errors on UNDO segments in the system table space. Only a 10 months old export was available.

Together with a consultant from Oracle we tried to get data from two damaged databases. For one DB, DUL could read the dictionary from the system data file, but could not read all the data from the user data files. The other DB also had a corrupt system data file, which meant that DUL was unable to read the dictionary and was unable to locate data from user data files.

We tried to recreate the system data file from the old export we still had, but DUL needs more info from the dictionary than only the data structure.

Retrieving data with DUL without a system dictionary would have been also possible, but from the data you will get, you must need to guess the table names, column names and data types. Without proper application knowledge, it’s like solving a jigsaw puzzle upside down.Unfortunately neither of the two databases was recovered for 100%. We can’t say how much data has been lost, but it looked liked Swiss cheese with more holes than cheese.

According to Oracle, DUL might be able to get all data back, but in this case the data files were to much damaged. A proper and tested backup/restore procedure would have been better (and cheaper) to start with.

Happy consulting!

Oracle DUL is an Oracle internal tool and not available to the public.

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