RMAN: Full = Level 0 ?
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Thread: RMAN: Full = Level 0 ?

  1. #1
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    I am a bit confused with RMAN books and documentation. Does a full RMAN backup copy more blocks than a Level 0 backup (by not skipping the empty blocks)? In the Oracle Documenation it says:

    "A full backup reads the entire file and copies all blocks into the backup set, skipping only datafile blocks that have never been used."

    In Metalink and Oracle Press books I have read the opposite, i.e., that only Level 0 skips the non-used blocks.

    What is true?


  2. #2
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    Thumbs up

    trust Metalink and Oracle Press books

  3. #3
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    There is a difference between blocks 'that have never been used' and the blocks that are 'currently empty'.
    IMHO,
    Full backup with RMAN copies all blocks upto the high-water point.
    Level 0 backup skips even those empty blocks which were used at one point (ie. empty blocks within the high water point ).
    At least that is what I understood from my humble beginner's knowledge.

    Raminder Singh

    Oracle Certified DBA: Oracle 8i, 9i


    Mail me at raminderahluwalia@rediffmail.com.

  4. #4
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    From your claim I understand what I suspect and believe: Level 0 backups less than full, i.e, level 0 skips the empty blocks within the HWM that have been used ones.

    (You may have blocks within the HWM which have never been used.)

    Still, is it true full RMAN backup skips that datafile blocks that have never been used?



  5. #5
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    Originally quoted by Julian
    You may have blocks within the HWM which have never been used
    How can this happen? Can you elaborate?

    Raminder Singh

    Oracle Certified DBA: Oracle 8i, 9i


    Mail me at raminderahluwalia@rediffmail.com.

  6. #6
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    Originally posted by julian

    Still, is it true full RMAN backup skips that datafile blocks that have never been used?

    Yes, correct.

    Extract from the oracle doc for 8.1.7
    A full backup reads the entire file and copies all blocks into the backup set, skipping only datafile blocks that have never been used. The server session does not skip blocks when backing up archived redo logs or control files.


    Sam

    Thanx
    Sam



    Life is a journey, not a destination!


  7. #7
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    Originally posted by Raminder
    Originally quoted by Julian
    You may have blocks within the HWM which have never been used
    How can this happen? Can you elaborate?
    Say, your table has 7 free lists. Each time the HWM for the segment is increased 40 free blocks are transfered. These blocks may not be used at once, so at first they will be empty.


  8. #8
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    Originally posted by sambavan
    Originally posted by julian

    Still, is it true full RMAN backup skips that datafile blocks that have never been used?

    Yes, correct.

    Extract from the oracle doc for 8.1.7
    A full backup reads the entire file and copies all blocks into the backup set, skipping only datafile blocks that have never been used. The server session does not skip blocks when backing up archived redo logs or control files.


    Sam

    Sam, so what does a Level-0 backup do less than a Full Backup? It skips the empty blocks that have been used at some point? Is that all?

    I have read the above from the Oracle Documentation but it conflicts information from some Oracle Press books and Metalink.



  9. #9
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    I, too, have read conflicting messages in the documentation. I have read/heard that a full backup will backup all blocks that have ever been used (whether they have data now or not). Then, supposedly, a level 0 will only backup the blocks that has data now. Here is a contridiction:

    Oracle8 Backup and Recovery Guide
    Chapter 7 Recovery Manager Concepts, page 7-14

    "An incremental level 0 backup occurs. This backups ALL blocks that have ever been used."

    In this same chapter you see full and level 0 to be used synonymously. I have had trouble with the size of my RMAN db output file, I received the suggestion to move from a full backup to a level 0. I haven't had a chance to test this yet. Would that make a difference?

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