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Question for ASM

978013 Newbie
Currently Being Moderated
Hi ! I'm just wondering if what would be the impact in the performance if for example I want to add a new a disk to ASM from the same physical disk or raid set? Like for example, I have a 400gb HDD and then at first I decided to allocate only 200gb to ASM and when the time comes that it will become full I will be needing to add the remaining 200gb. Would it have an impact especially in the performance because of course for oracle it reads it as a new physical disk but the real deal is that the added disk is just from the same raid set? And also one last thing, is it possible to resize the existing disk in the asm? I will appreciate every answer. Thanks in advance. :)

Edited by: Arjhay on Dec 4, 2012 7:25 PM
  • 1. Re: Question for ASM
    Osama_Mustafa Oracle ACE
    Currently Being Moderated
    it better to post your question here


    Oracle Discussion Forums » High Availability » Automatic Storage Management

    Arjhay wrote:
    Hi ! I'm just wondering if what would be the impact in the performance if for example I want to add a new a disk to ASM from the same physical disk or raid set? Like for example, I have a 400gb HDD and then at first I decided to allocate only 200gb to ASM and when the time comes that it will become full I will be needing to add the remaining 200gb.
    http://www.pythian.com/news/204/asm-multi-disk-performance/
    added disk is just from the same raid set? And also one last thing, is it possible to resize the existing disk in the asm?
    You just need to add new disk into existing diskgroup Or drop disks and resizie it .
  • 2. !
    978013 Newbie
    Currently Being Moderated
    Osama_mustafa wrote:
    it better to post your question here


    Oracle Discussion Forums » High Availability » Automatic Storage Management

    Arjhay wrote:
    Hi ! I'm just wondering if what would be the impact in the performance if for example I want to add a new a disk to ASM from the same physical disk or raid set? Like for example, I have a 400gb HDD and then at first I decided to allocate only 200gb to ASM and when the time comes that it will become full I will be needing to add the remaining 200gb.
    http://www.pythian.com/news/204/asm-multi-disk-performance/
    added disk is just from the same raid set? And also one last thing, is it possible to resize the existing disk in the asm?
    You just need to add new disk into existing diskgroup Or drop disks and resizie it .
    OK sir Thank you for the help!
  • 3. Re: Question for ASM
    Aman.... Oracle ACE
    Currently Being Moderated
    Arjhay wrote:
    Hi ! I'm just wondering if what would be the impact in the performance if for example I want to add a new a disk to ASM from the same physical disk or raid set? Like for example, I have a 400gb HDD and then at first I decided to allocate only 200gb to ASM and when the time comes that it will become full I will be needing to add the remaining 200gb. Would it have an impact especially in the performance because of course for oracle it reads it as a new physical disk but the real deal is that the added disk is just from the same raid set?
    It doesn't matter actually that the disk is a partition of the same "disk" or a new , standalone disk as when you would add the disk, ASM would start the rebalancing of the existing AU's over this newly added disk and since its a physical operation, it would have an impact on the database performance. There is workaround for it but as for your question, there would be an impact over the underlying db's performance.

    And also one last thing, is it possible to resize the existing disk in the asm? I will appreciate every answer. Thanks in advance. :)
    >

    I shall take a guess on it with the guess based on that the ASM doesn't do anything to the disk except using it, so the answer is a no but since its a guess so take it with a grain of salt and wait for others to jump in as well.

    HTH
    Aman....
  • 4. Re: Question for ASM
    978013 Newbie
    Currently Being Moderated
    Aman.... wrote:

    It doesn't matter actually that the disk is a partition of the same "disk" or a new , standalone disk as when you would add the disk, ASM would start the rebalancing of the existing AU's over this newly added disk and since its a physical operation, it would have an impact on the database performance. There is workaround for it but as for your question, there would be an impact over the underlying db's performance.
    Hi Aman! Thanks for the response, btw, may i know the workaround that you're telling? Can i see the link if theres any? And also, what may be the worst case scenario if ever I will add another disk in the ASM from the same physical disk or raid set?
  • 5. Re: Question for ASM
    Aman.... Oracle ACE
    Currently Being Moderated
    The workaround would be to set the rebalancing power limit to be 0 so that there won't be any starting when the disk is added. You may start using it right away but whenever the disk is going to be dropped, the drop operation would fail as it's not allowed as long as there is no rebalancing done. Can't think of any worst case scenario at the moment , sorry!

    Aman....
  • 6. Re: Question for ASM
    978013 Newbie
    Currently Being Moderated
    Ok, I'll test it first. Thank you so much Aman.
  • 7. Re: Question for ASM
    Girish Sharma Guru
    Currently Being Moderated
    Oracle Complete Version Info ?
    OS Complete Info ?

    So, that I may found in relevant docs.

    The first step in increasing the size of an ASM disk is to add extra storage capacity to the LUN. To use more space, the partition must be recreated. This operation is at the partition table level, and that table is stored in the first sectors of the disk. Changing the partition table does not affect the data. In Oracle Database 10g ASM, V$ASM_DISK shows the size of the disk when it was discovered by ASM; this size is reflected in the TOTAL_MB column. However, if the actual size of a disk is 250GB, but ASM uses (or allocates) only 200GB, you cannot determine the true disk size without querying the OS. Starting in Oracle Database 11g ASM, a new column in V$ASM_DISK called OS_MB gives the actual OS size of the disk. This column can aid in appropriately resizing the disk and prevent attempts to resize disks that cannot be resized.

    The general steps to resize an ASM disk are as follows:

    1. Resize LUN from storage array. This is usually a noninvasive operation.

    2. Query V$ASM_DISK for the OS_MB for the disk to be resized. If the OS or ASM do not see the new size, then review the steps from the host bus adapter (HBA) vendor to probe for new devices. In some cases, this may require a reboot.

    3. For 10.2.0.3 and earlier, you need to restart all ASM instances to ensure that they see the new LUN size. Oracle Database 11g ASM can detect new LUN sizes without restarting the instance. Issue ALTER DISKGROUP RESIZE DISK on one ASM instance. Note that a resize invokes an ASM rebalance.

    Page No. 158 Book Name:Oracle Automatic Storage Management: Under-the-Hood & Practical Deployment Guide Authors: Nitin Vengurlekar, Murali Vallath, Rich Long

    Regards
    Girish Sharma
  • 8. Re: Question for ASM
    Aman.... Oracle ACE
    Currently Being Moderated
    Thanks for the command and the notes Girish :) .

    Regards
    Aman....
  • 9. Re: Question for ASM
    Girish Sharma Guru
    Currently Being Moderated
    I am glad to see your appreciation but I did nothing, just copied the text from PDF and paste here. Truly speaking Sir, I never worked on ASM instance yet, shall try to learn and practice after reading relevant docs and this book on my new home PC. :)

    Regards
    Girish Sharma
  • 10. Re: Question for ASM
    978013 Newbie
    Currently Being Moderated
    Girish Sharma wrote:
    Oracle Complete Version Info ?
    OS Complete Info ?
    Hi Girish! Here are the details:

    PLATFORM/OS: Linux 2.6.18 194.el5 64bit
    DATABASE: 10.2.0.5.0 64bit

    I read everything you said and i find it very helpful, i will also test the steps that you have given.

    Thanks,
    Arjhay
  • 11. Re: Question for ASM
    Girish Sharma Guru
    Currently Being Moderated
    Then I think below link may be which you are looking :

    If you intend to use Automatic Storage Management for database storage on Linux, then Oracle recommends that you install the Automatic Storage Management library driver and associated utilities and use them to configure the devices that you want to include in an Automatic Storage Management disk group. If you do not use the Automatic Storage Management library driver, then you must bind each disk device that you want to use to a raw device. The following sections describe how to configure disks using each method:
    http://docs.oracle.com/cd/B19306_01/install.102/b15667/pre_install.htm#sthref436

    Regards
    Girish Sharma
  • 12. Re: Question for ASM
    Aman.... Oracle ACE
    Currently Being Moderated
    What's the configuration of the new pc?

    Aman....
  • 13. Re: Question for ASM
    Girish Sharma Guru
    Currently Being Moderated
    Not yet purchased, but I wish to have core i7, 64GB RAM, 1TB HDD (SSD). So that I may have Oracle Linux (downloading is running), 12c (coming soon for public..!!), ASM, RAC, Grid Control and DG and Virtualbox (Oracle) in which Windows 8 Ultimate 64 bit+Visual Studio 2012 and new (basic but not docs) questions on this forum as well... :)

    Please comment that PC is capable enough to have above s/w and technologies ?

    Regards
    Girish Sharma
  • 14. Re: Question for ASM
    Aman.... Oracle ACE
    Currently Being Moderated
    LOL with 64 GB you would be able to run the databases of many shops as well . Yep, sounds good!

    Aman....
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