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3 Replies Latest reply: Mar 25, 2013 6:43 PM by VamshiDamidi RSS

regarding to required_mirror_free_mb

Lonion Newbie
Currently Being Moderated
In V$ASM_DISKGROUP have a column named required_mirror_free_mb.

My question is :
1. what's required mirror ?
2. why asm reserve mirror space ?
3. how Oracle Automatic Storage Management (ASM) calculates the REQUIRED_MIRROR_FREE_MB ?
  • 1. Re: regarding to required_mirror_free_mb
    FreddieEssex Pro
    Currently Being Moderated
    http://docs.oracle.com/cd/B28359_01/server.111/b31107/asmdiskgrps.htm

    REQUIRED_MIRROR_FREE_MB indicates the amount of space that must be available in a disk group to restore full redundancy after the worst failure that can be tolerated by the disk group. The amount of space displayed in this column takes the effects of mirroring into account. The value is computed as follows:

    For a normal redundancy disk group, the value is the total raw space for all of the disks in the largest failure group. The largest failure group is the one with the largest total raw capacity. For example, if each disk is in its own failure group, then the value would be the size of the largest capacity disk.

    For a high redundancy disk group, the value is the total raw space for all of the disks in the two largest failure groups.
  • 2. Re: regarding to required_mirror_free_mb
    saratpvv Journeyer
    Currently Being Moderated
    Simillar thread... hope this will give correct answer

    confusion about required_mirror_free_mb in asm
  • 3. Re: regarding to required_mirror_free_mb
    VamshiDamidi Newbie
    Currently Being Moderated
    Let say i have a storage of 100G and i have insert data of 20G
    My ASM diskgroup is external redundancy
    then below are my values

    TOTAL_MB     =100G
    COLD_USED=20G
    FREE_MB=80G     
    REQUIRED_MIRROR_FREE_MB=0G     
    USABLE_FILE_MB     =80G


    For the same if my ASM diskgroup is normal redundancy then below are my values

    TOTAL_MB=100G
    COLD_USED=20G
    FREE_MB=80G
    REQUIRED_MIRROR_FREE_MB=40G approx
    USABLE_FILE_MB=40G approx

    Let me know if you have any concerns.

    Thanks,
    Vamshi .D

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