2 Replies Latest reply: Sep 12, 2012 10:18 AM by 934860 RSS

    ASM NORMAL REDUNDANCY QUESTION

    669464
      Dear all,

      Oracle document ASM NORMAL REDUNDANCY QUESTION [ID 1480954.1] is saying below statement,which i find difficult to understand line which is marked in italic.

      When determining the proper size of a diskgroup that will be protected with ASM redundancy, enough free space must exist in the diskgroup
      so that when a disk fails, it can automatically reconstruct the contents of the failed disk to another disk in the diskgroup. The database should remain online if enough space is available
      . The amount of space required to ensure ASM can restore redundancy following disk failure is in the column REQUIRED_MIRROR_FREE_MB in the V$ASM_DISKGROUP view. The amount of free space that can be safely used in a disk group, taking mirroring into account, and yet be able to restore redundancy after a disk failure is in the column USABLE_FILE_MB in the V$ASM_DISKGROUP view. USABLE_FILE_MB should always be greater than zero. If USABLE_FILE_MB falls below zero, then more disks should be added to the disk group.

      DOUBT:Why it needs to reconstruct the contents of failed disk to another disk in the diskgroup when it has the mirrored extents and i dont understand when disk itself is failed how it can access it and reconstruct its content on another disk.


      Regards
        • 1. Re: ASM NORMAL REDUNDANCY QUESTION
          Balazs Papp
          DOUBT:Why it needs to reconstruct the contents of failed disk to another disk in the diskgroup when it has the mirrored extents
          because the data that was on the failed disk isnt mirrored anymore (no extra copies) and in order to ensure normal redundancy level, a new mirror copy of the data will be constructed
          i dont understand when disk itself is failed how it can access it and reconstruct its content on another disk.
          from the still available, mirrored data

          to explain it simple:

          everything is stored with 2 copies (original + mirror)
          when 1 is lost, a new copy will be rebuilt from the other 1, so there will be 2 copies again
          • 2. Re: ASM NORMAL REDUNDANCY QUESTION
            934860
            Is mirrored ASM disk a feature of Oracle 10g ASM, or is it only 11g?