db_block_size and OS block size Correlation
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Thread: db_block_size and OS block size Correlation

  1. #1
    Join Date
    Jul 2000


    Hi everybody,

    I have a database used for datawarehousing. I set my
    db_block_size to 16K. I have heard conversations that
    a OS block size of 512 k will greatly improve reading performance for DSS on Widows NT. It is that so? What is the correlation between OS block size and db_block_size? Did anyone tried to optimize the I/O by changing OS block size from a default 64K to 512k? The database is Oracle 9i running on Windows 2000.


  2. #2
    Join Date
    May 2000
    Do you use Volume Manager for your disks?

    Volume Manager overrides the OS block size. For example, Veritas volume manager's default I/O block size is 8K.

  3. #3
    Join Date
    Jul 2000
    I am running Windows 2000 not Unix. I am not familiar
    with Unix volume manager.

  4. #4
    Join Date
    Apr 2001
    Louisville KY
    It has been my experience that if you use the 16K block size, you can/should adjust the data read amount to match the OS read buffer size (amount of data the io subsystem returns in 1 read.) If this is 512K, then a 32block multi-block-read-count would be appropriate.

    I am not sure what you mean by os block. Is it the read buffer or the cluster size (1000-512 byte sectors.)?
    A 512K disk block feels a little large. I don't know that I have seen a read amount over 32K at the io level.
    Joseph R.P. Maloney, CSP,CDP,CCP
    'The answer is 42'

  5. #5
    Join Date
    Jul 2000
    We ran 2 tests so far and the results are somewhat puzzling.
    #1) Low level format of our disk data array to 1024k blocks.
    Our Raid controller was set to 1024k stripe, (Raid0)
    Oracle DB_BLOCK_SIZE=16384 , DB_BLOCK_BUFFERS=500M

    #2) Low level format of our disk data array to 64k blocks.
    Same Oracle config.

    When building a identical tablespace on Item#2(driveset) it ran 15x faster than #1. I thought the larger the formatted blocksize on the disk itself, the quicker the throughput... and better oracle performance.. not true.. but why??

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