1 Reply Latest reply: Jan 3, 2013 4:50 AM by Dude! RSS

    Normal Redundancy and Physical Disks

    Omega3
      Grid Version : 11.2.0.3
      Platform : Oracle Enterprise Linux 6


      I am a bit confused about the term 'Two-way mirroring' in ASM documentation.


      If i want to store 1 Tera Byte of business data in an ASM diskgroup with NORMAL redundancy.
      Should I need 2 physical Disks of 1TB each ?
      or 
      Should I need 3 physical Disks of 1TB each ?
        • 1. Re: Normal Redundancy and Physical Disks
          Dude!
          ASM is not a software RAID. ASM works on the basis of file extents and provides data redundancy by using the free disk space of disk failure groups. By default, each disk is a failure group. For a 2-way (normal) mirror you need at least 2 disk failure groups; for 3-way (high) you need at least 3. You can also create a 2-way mirror using 3 disks, in which case data will be written in a round robin fashion. To have normal ASM redundancy in your example you need to have at least two 1 TB disks, but you can also use 3 and will have more space. You can also use an external RAID and use no (external) ASM redundancy, though ASM will give you better performance and flexibility since you can add disks to increase space without having to rebuild your storage.