Redo Log Files And Raid5
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  1. #1
    Join Date
    Sep 2006
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    Redo Log Files And Raid5

    Can anybody tell me
    Why it is not recommended not to put Redo Log Files on RAID5?

    Thanx in Advance

  2. #2
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    Sep 2002
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    if you saturate your cache you have a write penalty - redo logs needs to be written to as quickly as possible, else your clients wait

  3. #3
    Join Date
    Mar 2006
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    Wink Mirrored redolog files.

    Quote Originally Posted by M.Shakeel Azeem
    Can anybody tell me
    Why it is not recommended not to put Redo Log Files on RAID5?

    Thanx in Advance

    Hi ,

    the main reason is that if you get a redolog corrupt, the mirrored redolog will also be corrupt. If you set up a mirrored "by Oracle" (another phisical drive) set of redologs and one file in a set becomes corrupt, Oracle will not crash but will continue to work with the other set of redo logs until you fix the problem. Otherwise - when one redolog is corrupt, the mirrored by the operating system is corrupt as well and this could lead you to having the database crashing.

    The problem these days is that - like in my work I get a Windows server with all drives initially mirrored (typically only C: and D: ) and it's hard to follow Oracle recommendations.

    O hope this helps,

    Regards,
    Richard.
    Last edited by rysiekmus; 01-22-2007 at 06:22 AM. Reason: Add some text

  4. #4
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    Quote Originally Posted by rysiekmus
    Hi ,

    the main reason is that if you get a redolog corrupt, the mirrored redolog will also be corrupt. If you set up a mirrored "by Oracle" (another phisical drive) set of redologs and one file in a set becomes corrupt, Oracle will not crash but will continue to work with the other set of redo logs until you fix the problem. Otherwise - when one redolog is corrupt, the mirrored by the operating system is corrupt as well and this could lead you to having the database crashing.

    The problem these days is that - like in my work I get a Windows server with all drives initially mirrored (typically only C: and D: ) and it's hard to follow Oracle recommendations.

    O hope this helps,

    Regards,
    Richard.
    I would have to disagree with you Richard, and say that the main reason for not using RAID5 with redo logs is for the write overhead as previously stated.

    The fact that if you "get a redolog corrupt", you'll lose them all doesn't really compute with me. What type of corruption are you talking about? Corruption from data? If you are talking about hardware corruption then i'm not sure you have properly considered the benefits of RAID in that statement. If a disk fails then you hot swap it out (no data loss). If a RAID controller dies, the backup controller should kick in (no data loss). Please expand on your statements so that I fully understand.
    Assistance is Futile...

  5. #5
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    Depends on what your case is?

    In my case i have a very few users say less than 50 and my management gave me only raid5. So i have all the datafiles, redo logs and archive files in raid5 and spread over many disks.

    I never felt the write delays as the transactions are less than 5/sec during the peak load.

  6. #6
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    Colorado Springs
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    Quote Originally Posted by manasa
    In my case i have a very few users say less than 50 and my management gave me only raid5. So i have all the datafiles, redo logs and archive files in raid5 and spread over many disks.

    I never felt the write delays as the transactions are less than 5/sec during the peak load.
    You can monitor log_file_sync wait events to be sure about that.
    David Aldridge,
    "The Oracle Sponge"

    Senior Manager, Business Intelligence Development
    XM Satellite Radio
    Washington, DC

    Oracle ACE

  7. #7
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    well if you dont have a problem - well no problem

    but if you increase your io you may well - so something to think about

  8. #8
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    better raid 5 than no protection at all...
    Jeff Hunter
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