3 Replies Latest reply: Mar 25, 2013 8:43 PM by VamshiDamidi RSS

    regarding to required_mirror_free_mb

      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

          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
            Simillar thread... hope this will give correct answer

            confusion about required_mirror_free_mb in asm
            • 3. Re: regarding to required_mirror_free_mb
              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
              USABLE_FILE_MB     =80G

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

              REQUIRED_MIRROR_FREE_MB=40G approx
              USABLE_FILE_MB=40G approx

              Let me know if you have any concerns.

              Vamshi .D