file system vs ASM
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Thread: file system vs ASM

  1. #1
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    file system vs ASM

    Hi Friends,

    Is there any advantages of using file system on Oracle 10g DB as against ASM? Is it safe to start using ASM and forget the "file system" database set-up in my future Database Installations?


    Thanks a lot
    Behind The Success And Failure Of A Man Is A Woman

  2. #2
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    You can go for ASM...

    The Oracle notes itself saying that it is safe....

    With ASM, you don't have to create anything on the OS side; the feature will group a set of physical disks to a logical entity known as a diskgroup. A diskgroup is analogous to a striped (and optionally mirrored) filesystem, with important differences: it's not a general-purpose filesystem for storing user files and it's not buffered. Because of the latter, a diskgroup offers the advantage of direct access to this space as a raw device yet provides the convenience and flexibility of a filesystem.

    Logical volume managers typically use a function, such as hashing to map the logical address of the blocks to the physical blocks. This computation uses CPU cycles. Furthermore, when a new disk (or RAID-5 set of disks) is added, this typical striping function requires each bit of the entire data set to be relocated.

    In contrast, ASM uses a special Oracle Instance to address the mapping of the file extents to the physical disk blocks. This design, in addition to being fast in locating the file extents, helps while adding or removing disks because the locations of file extents need not be coordinated. This special ASM instance is similar to other filesystems in that it must be running for ASM to work and can't be modified by the user. One ASM instance can service a number of Oracle databases instances on the same server.

    This special instance is just that: an instance, not a database where users can create objects. All the metadata about the disks are stored in the diskgroups themselves, making them as self-describing as possible.

    So in a nutshell, what are the advantages of ASM?
    Disk Addition—Adding a disk becomes very easy. No downtime is required and file extents are redistributed automatically.
    I/O Distribution—I/O is spread over all the available disks automatically, without manual intervention, reducing chances of a hot spot.
    Stripe Width—Striping can be fine grained as in Redo Log Files (128K for faster transfer rate) and coarse for datafiles (1MB for transfer of a large number of blocks at one time).
    Buffering—The ASM filesystem is not buffered, making it direct I/O capable by design.
    Kernelized Asynch I/O—There is no special setup necessary to enable kernelized asynchronous I/O, without using raw or third-party filesystems such as Veritas Quick I/O.
    Mirroring—Software mirroring can be set up easily, if hardware mirroring is not available

  3. #3
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    Hi

    You have asked a very broad question.
    I don't think so if you use ASM you will forget filesystem.

    Many things depend upon oragnisation politics,existing infrastructure third party software etc etc...

    regards
    Hrishy

  4. #4
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    What Oracle did not add is performance.

    You can expect 20% to 30% less performance of using ASM.

  5. #5
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    Quote Originally Posted by tamilselvan
    What Oracle did not add is performance.
    You can expect 20% to 30% less performance of using ASM.
    huh? I'll be damned if I understand what you mean man; not your fault, your post got so close to gopu_g's posting that probably got infected
    Last edited by PAVB; 04-15-2008 at 12:28 PM.
    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.

  6. #6
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    Hi

    ASM peformance should be as good as raw or about the same as direct IO.

    regards
    Hrishy

  7. #7
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    Buffering—The ASM filesystem is not buffered, making it direct I/O capable by design
    could this be a performance issue?

    with ASM every physical write is really a physical write, with filesystem you have cache so every physical write could not be a real physical write.

  8. #8
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    please read my lips "ASM provides near raw device performance -period".

    You have read just half of what you had to read about buffering.
    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.

  9. #9
    Join Date
    Jul 2007
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    really?

    I believed I have read nothing about buffering, it's not bad as I thought...

    So if I have filesystem buffering, SAN caching etc etc

    How do they work all these buffering things together?

    I'm overbuffered?

    And If I have raw devices or ASM, so near direct I/O, SAN is no more caching?

  10. #10
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    best practice is to avoid double buffering so you are recommended to use Direct I/O and bypass filesystem buffer, instead you assign a larger Database Cache

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