ASM Question
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Thread: ASM Question

  1. #1
    Join Date
    Aug 2002
    Posts
    56

    ASM Question

    Hi,
    I had a question regarding ASM. We have 11.1.0.7 RAC databases runninig on ASM on RHEL5. The ASM disks are presented via an 3Par SAN. Now my understanding is that rebalance moves the hot blocks in ASM to another LUN. But in our case we are seeing that 1 LUN is significantly busier than the other in the same DG. This is even true for write operations. Now is there a way to reduce hot blocks / spread block within the DG? I understand that we can be tuning the sql in question, but since our is a muti-tenant env, its not about one or more sqls. Thats why I looking for some way of altering data placement within the DG.

    Other info:
    ASM Redundancy: External
    Striping: Coarse
    AU Size : 1mb

    TIA
    When in doubt ...go to the basics!!

  2. #2
    Join Date
    Mar 2007
    Location
    Ft. Lauderdale, FL
    Posts
    3,554
    ASM rebalance is meant to evenly distribute file extents across all disks on the particular diskgroup - which is not the same as saying that rebalance "rebalances" I/O load.

    You may get lucky and rebalance may help but for this to happen you should add storage to the particular diskgroup and pray, pray hard.

    Hot blocks are usually caused by application design, like an application reading the only row on a "status" kind of table each time something happens - if that "something" happens a lot then you get a hot block - I have seen this happening in a particular application where the designer created a table to generate sequence numbers instead of using a proper Oracle sequence.

    The only way to know why a particular block gets hot is to look at it, understand what is in there and why is being hit that much.

    Hope this helps.
    Pablo (Paul) Berzukov

    Author of Understanding Database Administration available at amazon and other bookstores.

    Disclaimer: Advice is provided to the best of my knowledge but no implicit or explicit warranties are provided. Since the advisor explicitly encourages testing any and all suggestions on a test non-production environment advisor should not held liable or responsible for any actions taken based on the given advice.

  3. #3
    Join Date
    Aug 2002
    Posts
    56
    Thanks Pablo. That clarifies!
    When in doubt ...go to the basics!!

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